onfiguring the internal and external oscillators · the internal and external oscillators. ......

30
Rev. 2.1 12/03 Copyright © 2003 by Silicon Laboratories AN102 AN102 C ONFIGURING THE I NTERNAL AND E XTERNAL O SCILLATORS Relevant Devices This application note applies to the following devices: C8051F000, C8051F001, C8051F002, C8051F005, C8051F006, C8051F010, C8051F011, C8051F012, C8051F012, C8051F015, C8051F016, C8051F017, C8051F018, C8051F019, C8051F020, C8051F021, C8051F022, C8051F023, C8051F040, C8051F041, C8051F042, C8051F043, C8051F060, C8051F061, C8051F062, C8051F063, C8051F120, C8051F121, C8051F122, C8051F123, C8051F124, C8051F125, C8051F126, C8051F127, C8051F206, C8051F220, C8051F221, C8051F226, C8051F230 and C8051F236. Introduction The purpose of this application note is to describe how to configure and use the internal and external oscillators. Configuration descriptions, setup examples, and sample code are provided. Key Points The internal oscillator in divide-by-8 mode is enabled and selected automatically when the device is reset. The system clock can be easily switched between the internal and external oscillators. It is legal to select the External Oscillator as the System Clock and disable the Internal Oscilla- tor in the same write, if possible on the device. If running off the external oscillator, it is legal to enable the internal oscillator and select the internal oscillator as the system clock in the same write. SYSCLK XTAL1 XTAL2 OSC Internal Clock Generator Input Circuit OSCXCN EN CRYSTAL RC CMOS AV+ C XTAL1 XTAL2 XTAL1 XTAL1 XTLVLD XOSCMD2 XOSCMD1 XOSCMD0 XFCN2 XFCN1 XFCN0 OSCICN MSCLKE IFRDY CLKSL IOSCEN IFCN1 IFCN0 AGND

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Page 1: ONFIGURING THE INTERNAL AND EXTERNAL OSCILLATORS · the internal and external oscillators. ... level clock source, ... then control can be switched to the high-frequency

Rev. 2.1 12/03 Copyright © 2003 by Silicon Laboratories AN102

AN102

CONFIGURING THE INTERNAL AND EXTERNAL OSCILLATORS

Relevant DevicesThis application note applies to the followingdevices:

C8051F000, C8051F001, C8051F002, C8051F005, C8051F006, C8051F010, C8051F011, C8051F012, C8051F012, C8051F015, C8051F016, C8051F017, C8051F018, C8051F019, C8051F020, C8051F021, C8051F022, C8051F023, C8051F040, C8051F041, C8051F042, C8051F043, C8051F060, C8051F061, C8051F062, C8051F063, C8051F120, C8051F121, C8051F122, C8051F123, C8051F124, C8051F125, C8051F126, C8051F127, C8051F206, C8051F220, C8051F221, C8051F226, C8051F230 and C8051F236.

IntroductionThe purpose of this application note is to describehow to configure and use the internal and externaloscillators. Configuration descriptions, setupexamples, and sample code are provided.

Key Points• The internal oscillator in divide-by-8 mode is

enabled and selected automatically when the device is reset.

• The system clock can be easily switched between the internal and external oscillators.

• It is legal to select the External Oscillator as the System Clock and disable the Internal Oscilla-tor in the same write, if possible on the device. If running off the external oscillator, it is legal to enable the internal oscillator and select the internal oscillator as the system clock in the same write.

SYSCLK

XTAL1

XTAL2

OSC

Internal ClockGenerator

InputCircuit

OSCXCN

EN

CRYSTAL

RC

CMOS

AV+C

XTAL1

XTAL2 XTAL1XTAL1

XT

LV

LDX

OS

CM

D2

XO

SC

MD

1X

OS

CM

D0

XF

CN

2X

FC

N1

XF

CN

0

OSCICN

MS

CL

KE

IFR

DY

CL

KS

LIO

SC

EN

IFC

N1

IFC

N0

AGND

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2 Rev. 2.1

• It is legal to change the frequency of the inter-nal oscillator while using the internal oscillator as the system clock.

• In all oscillator modes, /SYSCLK, a buffered version of the system clock, can be output on a port pin by enabling it in the Crossbar. On C8051F2xx devices, /SYSCLK may be enabled in the Port 1 MUX.

• If the Missing Clock Detector is enabled, a RESET will occur if the system clock drops below about 10 kHz.

• On some devices, the Crystal Oscillator Valid flag can be used to generate an interrupt when the crystal oscillator stabilizes, allowing the interrupt handler to switch to the external oscil-lator.

Clocking OptionsAll devices covered by this note have an internaland an external oscillator. The internal oscillatorfrequency is configurable from user software andhas four settings that that can divide the oscillatorfrequency by 1, 2, 4, or 8. It addition to the fourmain settings, some devices have a calibrated± 2 % internal oscillator with a fine-tunable fre-quency in steps of approximately 50 kHz. Theexternal oscillator provides even more flexibility infrequency selection, power consumption, and accu-racy using its 4 modes of operation.

The system clock can be freely switched betweenthe internal and external oscillators. Furthermore,you can leave the external oscillator enabled whilethe internal oscillator is selected to avoid startupdelays when the system clock is switched back tothe external oscillator.

The operation of the internal and external oscilla-tors is governed by SFR registers described in the‘Oscillators’ chapter of the appropriate datasheet.

Internal OscillatorAt reset, the internal oscillator divided by 8 isselected as the system clock. The internal oscillator

settings and typical frequencies are shown inTable 1 . The internal oscillator divide factor can bechanged on the fly by changing the IFCN bits. Thefrequency change happens almost instantaneously

The power consumption of the internal oscillatoritself is independent of the selected frequency;however, the power consumption of the entiredevice is frequency dependent.

The accuracy of the internal oscillator is ± 20 %across process, power supply, and temperature vari-ations on devices with an uncalibrated 16 MHzoscillator and ± 2 % on devices with a calibrated24.5 MHz oscillator.

External OscillatorThe external oscillator is highly configurable,offering many choices to the system designer. Thetime base can be derived from an external CMOS-level clock source, an attached crystal or ceramicresonator, an attached RC combination, or an exter-nal capacitor.

External CMOS Clock Mode

The system clock can be supplied from an externalCMOS-level clock source tied to the XTAL1 pin,such as a crystal oscillator module or the clock sig-

Table 1. Internal Oscillator Frequency Control Bits in the OSCICN Register

IFCN

Typical Frequency

(16 MHz Oscillator)

Typical Frequency (24.5 MHz Calibrated Osciillator)

00b 2 MHz 3.0625 MHz

01b 4 MHz 6.125 MHz

10b 8 MHz 12.25 MHz

11b 16 MHz 24.5 MHz

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Rev. 2.1 3

nal from another MCU. Note: the XTAL1 pin is NOT 5V-tolerant.

External Crystal Mode

In general, a crystal is called for when an accuratetime base is needed, for example when the absolutesampling rate of the ADC is critical or a standardUART baud rate must be generated. Note that ondevices with a calibrated 24.5 MHz internal oscil-lator, a crystal is not needed for UART communica-tion. Alternately, a low-frequency tuning-forkcrystal, e.g. a 32.768 kHz watch crystal, can beused to operate the device in a low-power mode,then control can be switched to the high-frequencyinternal oscillator as required by the system.

The accuracy and stability of the crystal oscillatoris governed almost exclusively by the attachedcrystal or ceramic resonator, provided that the load-ing capacitance parameters and oscillator drivelevel are set appropriately.

The crystal oscillator circuit is designed to be usedwith parallel-mode-specified crystals.

External RC

The external oscillator time base can also bederived from an external series RC combination

connected as shown in Figure 1. When the capaci-tor voltage (Vc) is less than VDD/3, the capacitorcharges through the resistor. Once the capacitorvoltage reaches VDD/3, the comparator creates apath to AGND and discharges the capacitor.

This operation produces a saw-tooth type wave-form at XTAL1, shown in Figure 2, whose periodis dominated by the rise time of the voltage acrossthe cap; the discharge time is less than 10 ns for a100 pF capacitor. The output of the comparator isbuffered and fed to a divide-by-two stage, the out-put of which becomes the system clock.

The accuracy of the time base in external RC modeis dominated by the tolerances of the R and C com-ponents.

XTAL1+-

VDD/3

VDD

+

-

Vc

C

R

Figure 1. RC Mode Overview

VDD

VDD/3

Time

Vc

Figure 2. RC Mode Waveform Generation

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4 Rev. 2.1

External C Mode

This mode is similar in operation to the externalRC mode above, except the charging current for thecapacitor is supplied by an internal programmablecurrent source at XTAL2. This is the least accuratetime base mode; however, it is the most flexible inthat a single passive component can provide up toeight different operating frequencies, the highestfrequency being almost a factor of 3000 greaterthan the lowest frequency.

The external oscillator in C mode generates a sig-nal by constantly charging and discharging thecapacitor connected to XTAL2. As Figure 3 shows,the capacitor charges linearly from a constant cur-rent source. When the voltage on the capacitorreaches VDD/3, the comparator creates a path toground, discharging the capacitor. Once the capaci-tor is discharged, the comparator opens the switchand the cycle repeats. The resulting waveform isshown in Figure 4.

The accuracy of the time base in external C mode isdominated by the tolerance on the capacitor and theaccuracy of the internal current source at XTAL2.The accuracy of the internal current source is on

the order of ± 30 % across process, power supply,and temperature variations.

Internal Oscillator Configuration ExampleAt reset, the internal oscillator divided by 8 isselected as the system clock.

Hardware Connection: If the system design usesthe internal oscillator exclusively AND does notuse the external oscillator, the XTAL1 pin shouldbe grounded externally as shown in Figure 5, orgrounded internally by setting the XOSCMD bits(OSCXCN.6-4) to '000'. If the system calls for hav-ing the /RST line of the device held low for longperiods of time, then grounding XTAL1 externallyis recommended.

XTAL1+-

VDD/3

VDD

+

-

Vc

C

Figure 3. C Mode Overview

Figure 4. C Mode Waveform Generation

VDD

VDD/3

Time

Vc

XTAL1

XTAL2

InternalOscillator

AGND

Figure 5. Optional Internal Oscillator Connection

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Rev. 2.1 5

The IFCN bits (OSCICN.1-0) program the internaloscillator frequency. Four divide settings are select-able as shown in Table 1 . If the device has a cali-brated 24.5 MHz internal oscillator, the frequencymay be fine-tuned by incrementing or decrement-ing the OSCICL register.

The startup and stabilization time for the internaloscillator is nearly instantaneous. Also, the internaloscillator’s frequency can be changed arbitrarily atany time. Since the internal oscillator stabilizes atits newly programmed frequency before the nextinstruction is executed, IFRDY polling is notrequired.

External Oscillator Configuration ExamplesThe external oscillator supports four different con-figurations: CMOS clock, crystal , RC, and Cmodes. The external oscillator can be configuredusing the OSCXCN register. Once the externaloscillator has been configured and has stabilized,the system clock can switch from the internal oscil-lator to the external oscillator using the CLKSLbit(s). Check the appropriate datasheet for moreinformation and the location of the CLKSL bit(s).

In crystal-based designs, it can take up to severalmilliseconds to start the crystal oscillator, depend-ing on the crystal frequency. Slower crystals tend tohave a longer startup time than faster crystals. TheXTLVLD (Crystal Oscillator Valid) flag can beused to determine when the external oscillator hasstabilized.

In external RC and external C modes, the startuptime of the external oscillator is instantaneous.

External CMOS ClockThe external oscillator clock can be supplied froman external CMOS-level source tied to the XTAL1input. In this configuration, XTAL2 should be leftfloating, as shown in Figure 6. The SYSCLK fre-

quency can be derived from the incoming signal as-is, or passed through a divide-by-two stage.

Note: Unlike some port I/O pins, the XTAL1and XTAL2 pins are NOT 5-V tolerant. Thevoltage at these pins should be kept betweenAV+ and AGND.

External CrystalThe external oscillator timebase can be derivedfrom a crystal or ceramic resonator connectedacross the XTAL1 and XTAL2 pins, as shown inFigure 7. The external oscillator can be configuredto to use the crystal frequency as-is, or divided bytwo. Also, XFCN should be set based on the crystalfrequency as discussed later in the text.

The XTLVLD (Crystal Oscillator Valid) flag can beused to determine when the external oscillator has

XTAL1

XTAL2

CMOSClock

Source

Figure 6. External CMOS Clock Connection

XTAL1

XTAL2

ExternalCrystal

AGND

X1

Cx1

Cx2

10 M

Figure 7. External

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AN102

6 Rev. 2.1

stabilized. The XTLVLD detection circuit requiresa settling time to acheive proper bias. Introducing a1 ms delay between enabling the oscillator andchecking the XTLVLD flag will prevent a prema-ture switch to the external oscillator as the systemclock. Switching to the external oscillator before ithas fully stabilized can cause unpredicable behav-ior.

Note: the loading capacitors (Cx1 and Cx2 inFigure 7) should be tied to the analog ground plane.Also note that the feedback resistor for the crys-tal oscillator inverter is supplied on-chip, mak-ing an external resistor unnecessary.

Crystal Startup Procedure

1. Configure the OSCXCN register to select thedesired external oscillator mode.

2. Wait at least 1ms.

3. Poll for XTLVLD => ‘1’.

4. Switch the system clock to the external oscilla-tor.

Determining XFCN

XFCN controls the drive level of the crystal oscil-lator driver. In essence, the drive level should bestrong enough to excite the crystal to oscillation,but not so strong as to stress the crystal to cause itto degrade prematurely.

For 3 MHz crystals and above, degradation basedon an XFCN setting that is too high is typically notan issue, and the maximum XFCN value can beused, though this will result in a higher operatingcurrent for the oscillator. For low-frequency tun-ing-fork crystals, 32.768 kHz and 100 kHz forexample, overdriving the crystal does present areliability concern. Additionally, if the drive levelis too high, the tuning-fork crystals may not oscil-late at all.

If the design uses a normal quartz crystal, Table 2 and Table 3 can be used to quickly determineXFCN based on the crystal frequency. .

Table 2. Crystal Mode XFCN Selection for ‘F00x, ‘F01x, ‘F02x and ‘F2xx Devices

XFCN Crystal Frequency

000b f < 12 kHz

001b 12 kHz < f 30 kHz

010b 30 kHz < f 95 kHz

011b 95 kHz < f 270 kHz

100b 270 kHz < f 720 kHz

101b 720 kHz < f 2.2 MHz

110b 2.2 MHz < f 6.7 MHz

111b f > 6.7 MHz

Table 3. Crystal Mode XFCN Selection for ‘F04x, ‘F06x, and ‘F12x Devices

XFCN Crystal Frequency

000b f < 32 kHz

001b 32 kHz < f 84 kHz

010b 84 kHz < f 225 kHz

011b 225 kHz < f 590 kHz

100b 590 kHz < f 1.5 MHz

101b 1.5 kHz < f 4 MHz

110b 4 MHz < f 10 MHz

111b 10 MHz < f 30 MHz

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AN102

Rev. 2.1 7

External RC NetworkFigure 5 shows the connection diagram for externalRC mode. Note that the series RC connection ismade between the analog power supply and analogground. Equation 1 gives the external oscillator fre-quency in RC mode.

To configure the device for RC mode, the ExternalOscillator Mode bits in the OSCXCN registershould be set to ‘10x’. This setting is valid for bothRC and C modes. When using these modes, aninternal divide-by-two stage is always enabled andis accounted for in Equation 1. Furthermore, theXFCN drive current selection should be set accord-

ing to Table 4 .

XFCN can always be set to a number higher thanindicated in Table 3, but will result in a higheroperating current for the oscillator. If XFCN is settoo low, the oscillator frequency will be lower thanpredicted by Equation 1.

Note: the startup time for the external oscillatorin RC mode is nearly instantaneous. TheXTLVLD flag is undefined in this mode.

The supplied capacitor should be between 10 pFand 100 pF, keeping in mind that at lower capaci-tance values the parasitic capacitance will have agreater impact on the final frequency. We illustratewith a few examples:

RC Example: 100 kHZ

We start with C = 33 pF. The total capacitanceincluding stray capacitance is 33 + 6, or 39 pF.

AV+

XTAL1

XTAL2

AGND

R

C

Figure 8. External RC Connection

Equation 1. External Oscillator Frequency in RC Mode

Fosc1.23

310R C

-----------------------=

Where:

Fosc external oscillator frequency in MHz=

R resistor value in k=

C capacitor value in pF=

Table 4. RC Mode XFCN Selection

XFCN Oscillation Frequency

000b f < 25 kHz

001b 25 kHz < f50 kHz

010b 50 kHz < f 100 kHz

011b 100 kHz < f 200 kHz

100b 200 kHz < f 400 kHz

101b 400 kHz < f 800 kHz

110b 800 kHz < f 1.6 MHz

111b 1.6 MHz < f 3.2 MHz

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8 Rev. 2.1

Assuming we want a frequency of oscillation of100 kHz, we solve Equation 3 to find R:

From Table 3, we set XFCN to at least '010'.

RC Example: 3.2 MHz

It is possible to operate the external oscillator inRC mode at frequencies greater than 3.2 MHz, butthis practice is not recommended. There will be asignificant deviation of the oscillation frequencyfrom the equation-predicted value as the frequencyincreases. Specifically, the actual frequency ofoscillation will tend to be lower than the predictedvalue due to fixed internal delays, which becomeappreciable as the oscillation period decreases.

Using a 33 pF capacitor which results in a totalcapacitance of 39 pF, we solve Equation 1 to findR:

From Table 4 , we set XFCN to a value of '111'.

RC Example: 1 kHz

If A/D converter performance is not critical, thesystem clock frequency can be made arbitrarilyslow, provided that the missing clock detector is

disabled. If the missing clock detector is enabled, itwill generate a system reset if the system clockfalls below about 10 kHz.

In this example, we use a C value of 100 pF, result-ing in a total capacitance of 106 pF. Solving Equa-tion 3 for R:

From Table 3, XFCN can be set to '000'.

External CapacitorFigure 6 shows the connections for external Cmode. Note that the XTAL1 and XTAL2 pins aretied together, and that the supplied capacitor is tiedbetween the XTAL pins and the analog groundplane. Equation 2 gives the external oscillator fre-quency in C mode.

Table 5 lists K Factor vs. XFCN setting.

External C mode is similar in operation to externalRC mode, except that the charging current for thecapacitor is supplied by a programmable currentsource at XTAL2. The supplied capacitor should bebetween 10 pF and 100 pF, keeping in mind that at

Fosc1.23

310R C

-----------------------=

R1.23

310Fosc C------------------------=

R1.23

3100.1 39-----------------------=

R 315 k=

Fosc1.23

310R C

-----------------------=

R1.23

310Fosc C------------------------=

R1.23

3103.2 39-----------------------=

R 9.86 k=

Fosc1.23

310R C

-----------------------=

R1.23

310Fosc C------------------------=

R1.23

3100.001 106-------------------------------=

R 11.6 M=

XTAL1

XTAL2

C AGND

Figure 9. External Capacitor Connection

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Rev. 2.1 9

lower capacitance values the parasitic capacitancewill have a greater impact on the final frequency.

The actual frequency of oscillation is highly vari-able due to capacitor tolerance, parasitic capaci-tance, power supply voltage, and the variance ofthe internal current source, which is about ± 30 %.

Note: the startup time for the external oscillatorin C mode is nearly instantaneous. TheXTLVLD flag is undefined in this mode.

We illustrate external C mode with some examples:

C Example: 100 kHz

Assuming a 3.0V analog power supply and a 33 pFexternal capacitor, the total capacitance includingparasitic capacitance is 39 pF. We solve Equation 2for KF:

Referencing Table 5 , the closest KF value is 13,for a device that has a 16 MHz internal oscillator.Solving Equation 2 with a KF of 13 yields an oscil-lation frequency of about 111 kHz. Increasing ourcapacitor value to 37 pF (43 pF total) and solvingEquation 2 for frequency, we find that we canachieve 101 kHz. We set XFCN to '011' to select aKF value of 13.

Adjacent XFCN values result in K Factors whichare about a factor of three apart. For example,increasing XFCN to '011' in the above examplewould increase the oscillation frequency fromabout 100 kHz to about 300 kHz.

Setting XFCN to its highest value '111', results in aKF of 1400. Using this setting with the abovecapacitance results in a frequency of oscillation ofabout 10 MHz as predicted by Equation 4. As inthe external RC mode, the equations are accuratefor frequencies that are 3 MHz and below, andbecome less accurate as the frequency increases.

Table 5. C Mode XFCN Selection

XFCN

KF for ‘F00x, ‘F01x, ‘F02x,

and ‘F2xx Devices

KF for ‘F04x, ‘F06x, and

‘F12x Devices

000b 0.44 0.87

001b 1.4 2.6

010b 4.4 7.7

011b 13 22

100b 38 65

101b 100 180

110b 420 664

111b 1400 1590

Equation 2. Oscillator Frequency in C Mode

FoscKF

C AV+----------------------=

Where:

Fosc external oscillator frequency MHz=

KF The K Factor, a unit-less quantity=

C capacitor value in pF (includes stray capacitance=

AV+ analog power supply voltage in Volts=

KF Fosc C AV+ =

KF 0.1 39 3.0 =

KF 11.7=

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10 Rev. 2.1

C Example: 3 MHz

Using an external capacitor of 50 pF (56 pF totalcapacitance) and 3.0 V AV+, we solve Equation 4for KF:

The closest KF in Table 4 for devices with a16 MHz internal oscillator is 420. This results in afrequency of oscillation around 2.5 MHz so we setXFCN to '110'.

KF Fosc C AV+ =

KF 3 56 3.0 =

KF 504=

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Rev. 2.1 11

Software Configuration ExamplesThe following examples show how to configure the internal and external oscillators on each device fam-ily.

C8051F00x and C8051F01x Example//-----------------------------------------------------------------------------// F0xx_Osc_Init.c//-----------------------------------------------------------------------------// Copyright 2003 Cygnal Integrated Products, Inc.//// AUTH: FB// DATE: 27 DEC 02//// This program shows an example of configuring the internal // and external oscillators. //// Target: C8051F00x and C8051F01x// Tool chain: KEIL C51 6.03 / KEIL EVAL C51//

//-----------------------------------------------------------------------------// Includes//-----------------------------------------------------------------------------

#include <c8051f000.h> // SFR declarations

//-----------------------------------------------------------------------------// 16-bit SFR Definitions for ‘F00x//-----------------------------------------------------------------------------

sfr16 DP = 0x82; // data pointersfr16 TMR3RL = 0x92; // Timer3 reload valuesfr16 TMR3 = 0x94; // Timer3 countersfr16 ADC0 = 0xbe; // ADC0 datasfr16 ADC0GT = 0xc4; // ADC0 greater than windowsfr16 ADC0LT = 0xc6; // ADC0 less than windowsfr16 RCAP2 = 0xca; // Timer2 capture/reloadsfr16 T2 = 0xcc; // Timer2sfr16 DAC0 = 0xd2; // DAC0 datasfr16 DAC1 = 0xd5; // DAC1 data

//-----------------------------------------------------------------------------// Function PROTOTYPES//-----------------------------------------------------------------------------

void SYSCLK_IntOsc_Init (void);void SYSCLK_Crystal_Init (void);void SYSCLK_C_RC_Init (void);void SYSCLK_CMOS_Init (void);

//-----------------------------------------------------------------------------// MAIN Routine//-----------------------------------------------------------------------------

void main (void) {

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12 Rev. 2.1

WDTCN = 0xde; // disable watchdog timer WDTCN = 0xad; // select one of the following functions to initialze the system clock SYSCLK_IntOsc_Init ();// SYSCLK_Crystal_Init (); // SYSCLK_C_RC_Init (); // SYSCLK_CMOS_Init ();

while (1);}

//-----------------------------------------------------------------------------// Initialization Subroutines//-----------------------------------------------------------------------------//-----------------------------------------------------------------------------// SYSCLK_IntOsc_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use the internal oscillator// at its maximum frequency.//void SYSCLK_IntOsc_Init (void){ OSCICN = 0x87; // Set internal oscillator to // maximum frequency and enable missing // clock detector}

//-----------------------------------------------------------------------------// SYSCLK_Crystal_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use a 22.1184MHz crystal// as its clock source. Assumes a 22.1184 MHz crystal and associated loading// capacitors are connected at XTAL1 and XTAL2.//void SYSCLK_Crystal_Init (void){ int i; // delay counter

OSCXCN = 0x67; // start external oscillator with // 22.1184MHz crystal

for (i=0; i < 256; i++) ; // XTLVLD blanking interval (>1ms)

while (!(OSCXCN & 0x80)) ; // Wait for crystal osc. to settle

OSCICN = 0x88; // select external oscillator as SYSCLK // source and enable missing clock // detector}

//-----------------------------------------------------------------------------// SYSCLK_C_RC_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use an external RC network

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Rev. 2.1 13

// or a single capacitor as its clock source. Assumes an RC network is // connected to XTAL1 or a single capacitor is connected to XTAL1 and// XTAL2.//void SYSCLK_C_RC_Init (void){ OSCXCN = 0x47; // start external oscillator in // C/RC mode with XFCN = 7

OSCICN = 0x88; // select external oscillator as SYSCLK // source and enable missing clock // detector}

//-----------------------------------------------------------------------------// SYSCLK_CMOS_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to the external oscillator in// CMOS clock mode. Assumes a CMOS clock generator is connected to XTAL1.//void SYSCLK_CMOS_Init (void){ OSCXCN = 0x20; // start external oscillator in // CMOS clock mode. OSCICN = 0x88; // select external oscillator as SYSCLK // source and enable missing clock // detector}

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14 Rev. 2.1

C8051F02x Example//-----------------------------------------------------------------------------// F02x_Osc_Init.c//-----------------------------------------------------------------------------// Copyright 2003 Cygnal Integrated Products, Inc.//// AUTH: FB// DATE: 27 DEC 02//// This program shows an example of configuring the internal// and external oscillators.//// Target: C8051F02x// Tool chain: KEIL C51 6.03 / KEIL EVAL C51//

//-----------------------------------------------------------------------------// Includes//-----------------------------------------------------------------------------

#include <c8051f020.h> // SFR declarations

//-----------------------------------------------------------------------------// 16-bit SFR Definitions for ‘F02x//-----------------------------------------------------------------------------

sfr16 DP = 0x82; // data pointersfr16 TMR3RL = 0x92; // Timer3 reload valuesfr16 TMR3 = 0x94; // Timer3 countersfr16 ADC0 = 0xbe; // ADC0 datasfr16 ADC0GT = 0xc4; // ADC0 greater than windowsfr16 ADC0LT = 0xc6; // ADC0 less than windowsfr16 RCAP2 = 0xca; // Timer2 capture/reloadsfr16 T2 = 0xcc; // Timer2sfr16 RCAP4 = 0xe4; // Timer4 capture/reloadsfr16 T4 = 0xf4; // Timer4sfr16 DAC0 = 0xd2; // DAC0 datasfr16 DAC1 = 0xd5; // DAC1 data

//-----------------------------------------------------------------------------// Global CONSTANTS//-----------------------------------------------------------------------------

sbit LED = P1^6; // LED=’1’ means ONsbit SW1 = P3^7; // SW1=’0’ means switch pressed

//-----------------------------------------------------------------------------// Function PROTOTYPES//-----------------------------------------------------------------------------

void SYSCLK_IntOsc_Init (void);void SYSCLK_Crystal_Init (void);void SYSCLK_C_RC_Init (void);void SYSCLK_CMOS_Init (void);

//-----------------------------------------------------------------------------// MAIN Routine//-----------------------------------------------------------------------------

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void main (void) {

WDTCN = 0xde; // disable watchdog timer WDTCN = 0xad;

// select one of the following functions to initialze the system clock SYSCLK_IntOsc_Init ();// SYSCLK_Crystal_Init ();// SYSCLK_C_RC_Init ();// SYSCLK_CMOS_Init ();

while (1);}

//-----------------------------------------------------------------------------// Initialization Subroutines//-----------------------------------------------------------------------------//-----------------------------------------------------------------------------// SYSCLK_IntOsc_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use the internal oscillator// at its maximum frequency.//void SYSCLK_IntOsc_Init (void){ OSCICN = 0x87; // Set internal oscillator to // maximum frequency and enable missing // clock detector}

//-----------------------------------------------------------------------------// SYSCLK_Crystal_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use a 22.1184MHz crystal// as its clock source. Assumes a 22.1184 MHz crystal and associated loading// capacitors are connected at XTAL1 and XTAL2.//void SYSCLK_Crystal_Init (void){ int i; // delay counter

OSCXCN = 0x67; // start external oscillator with // 22.1184MHz crystal

for (i=0; i < 256; i++) ; // XTLVLD blanking interval (>1ms)

while (!(OSCXCN & 0x80)) ; // Wait for crystal osc. to settle

OSCICN = 0x88; // select external oscillator as SYSCLK // source and enable missing clock // detector}

//-----------------------------------------------------------------------------// SYSCLK_C_RC_Init//-----------------------------------------------------------------------------

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//// This routine initializes the system clock to use an external RC network// or a single capacitor as its clock source. Assumes an RC network is// connected to XTAL1 or a single capacitor is connected to XTAL1 and// XTAL2.//void SYSCLK_C_RC_Init (void){ OSCXCN = 0x47; // start external oscillator in // C/RC mode with XFCN = 7

OSCICN = 0x88; // select external oscillator as SYSCLK // source and enable missing clock // detector}

//-----------------------------------------------------------------------------// SYSCLK_CMOS_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to the external oscillator in// CMOS clock mode. Assumes a CMOS clock generator is connected to XTAL1.//void SYSCLK_CMOS_Init (void){ OSCXCN = 0x20; // start external oscillator in // CMOS clock mode.

OSCICN = 0x88; // select external oscillator as SYSCLK // source and enable missing clock // detector}

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C8051F04x Example//-----------------------------------------------------------------------------// F04x_Osc_Init.c//-----------------------------------------------------------------------------// Copyright 2003 Cygnal Integrated Products, Inc.//// AUTH: FB// DATE: 27 DEC 02//// This program shows an example of configuring the internal// and external oscillators.//// Target: C8051F04x// Tool chain: KEIL C51 6.03 / KEIL EVAL C51//

//-----------------------------------------------------------------------------// Includes//-----------------------------------------------------------------------------

#include <c8051f040.h> // SFR declarations

//-----------------------------------------------------------------------------// Function PROTOTYPES//-----------------------------------------------------------------------------

void SYSCLK_IntOsc_Init (void);void SYSCLK_Crystal_Init (void);void SYSCLK_C_RC_Init (void);void SYSCLK_CMOS_Init (void);

//-----------------------------------------------------------------------------// MAIN Routine//-----------------------------------------------------------------------------

void main (void) {

WDTCN = 0xde; // disable watchdog timer WDTCN = 0xad;

// select one of the following functions to initialze the system clock SYSCLK_IntOsc_Init ();// SYSCLK_Crystal_Init ();// SYSCLK_C_RC_Init ();// SYSCLK_CMOS_Init ();

while (1);}

//-----------------------------------------------------------------------------// Initialization Subroutines//-----------------------------------------------------------------------------//-----------------------------------------------------------------------------// SYSCLK_IntOsc_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use the internal oscillator// at its maximum frequency.

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//void SYSCLK_IntOsc_Init (void){ char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page SFRPAGE = CONFIG_PAGE; // Set SFR Page

OSCICN = 0x83; // Set internal oscillator to // maximum frequency

CLKSEL = 0x00; // Select internal oscillator as // SYSCLK source

SFRPAGE = SFRPAGE_SAVE; // Restore SFR page}

//-----------------------------------------------------------------------------// SYSCLK_Crystal_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use an 22.1184MHz crystal// as its clock source. Assumes a 22.1184 MHz crystal and associated loading// capacitors are connected at XTAL1 and XTAL2.//void SYSCLK_Crystal_Init (void){ int i; // delay counter char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page SFRPAGE = CONFIG_PAGE; // Set SFR Page

OSCXCN = 0x67; // start external oscillator with // 22.1184MHz crystal (XFCN = 7)

for (i=0; i < 256; i++) ; // XTLVLD blanking interval (>1ms)

while (!(OSCXCN & 0x80)) ; // Wait for crystal osc. to settle

SFRPAGE = LEGACY_PAGE; RSTSRC = 0x04; // enable missing clock detector

SFRPAGE = CONFIG_PAGE; CLKSEL = 0x01; // select external oscillator as SYSCLK // source

OSCICN = 0x00; // disable internal oscillator

SFRPAGE = SFRPAGE_SAVE; // Restore SFR page}

//-----------------------------------------------------------------------------// SYSCLK_C_RC_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use an external RC network// or a single capacitor as its clock source. Assumes an RC network is// connected to XTAL1 or a single capacitor is connected to XTAL1 and// XTAL2.//

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void SYSCLK_C_RC_Init (void){ char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page SFRPAGE = CONFIG_PAGE; // Set SFR Page

OSCXCN = 0x47; // start external oscillator in // C/RC mode with XFCN = 7 SFRPAGE = LEGACY_PAGE; RSTSRC = 0x04; // enable missing clock detector

SFRPAGE = CONFIG_PAGE; CLKSEL = 0x01; // select external oscillator as SYSCLK // source

OSCICN = 0x00; // disable internal oscillator

SFRPAGE = SFRPAGE_SAVE; // Restore SFR page}

//-----------------------------------------------------------------------------// SYSCLK_CMOS_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to the external oscillator in// CMOS clock mode. Assumes a CMOS clock generator is connected to XTAL1.//void SYSCLK_CMOS_Init (void){ char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page SFRPAGE = CONFIG_PAGE; // Set SFR Page

OSCXCN = 0x20; // start external oscillator in // CMOS clock mode.

SFRPAGE = LEGACY_PAGE; RSTSRC = 0x04; // enable missing clock detector

SFRPAGE = CONFIG_PAGE; CLKSEL = 0x01; // select external oscillator as SYSCLK // source

OSCICN = 0x00; // disable internal oscillator

SFRPAGE = SFRPAGE_SAVE; // Restore SFR page}

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20 Rev. 2.1

C8051F06x Example//-----------------------------------------------------------------------------// F06x_Osc_Init.c//-----------------------------------------------------------------------------// Copyright 2003 Cygnal Integrated Products, Inc.//// AUTH: FB// DATE: 27 DEC 02//// This program shows an example of configuring the internal// and external oscillators.//// Target: C8051F06x// Tool chain: KEIL C51 6.03 / KEIL EVAL C51//

//-----------------------------------------------------------------------------// Includes//-----------------------------------------------------------------------------

#include <c8051f060.h> // SFR declarations

//-----------------------------------------------------------------------------// Function PROTOTYPES//-----------------------------------------------------------------------------

void SYSCLK_IntOsc_Init (void);void SYSCLK_Crystal_Init (void);void SYSCLK_C_RC_Init (void);void SYSCLK_CMOS_Init (void);

//-----------------------------------------------------------------------------// MAIN Routine//-----------------------------------------------------------------------------

void main (void) {

WDTCN = 0xde; // disable watchdog timer WDTCN = 0xad;

// select one of the following functions to initialze the system clock SYSCLK_IntOsc_Init ();// SYSCLK_Crystal_Init ();// SYSCLK_C_RC_Init ();// SYSCLK_CMOS_Init ();

while (1);}

//-----------------------------------------------------------------------------// Initialization Subroutines//-----------------------------------------------------------------------------//-----------------------------------------------------------------------------// SYSCLK_IntOsc_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use the internal oscillator// at its maximum frequency.

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//void SYSCLK_IntOsc_Init (void){ char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page SFRPAGE = CONFIG_PAGE; // Set SFR Page

OSCICN = 0x83; // Set internal oscillator to // maximum frequency

CLKSEL = 0x00; // Select internal oscillator as // SYSCLK source

SFRPAGE = SFRPAGE_SAVE; // Restore SFR page}

//-----------------------------------------------------------------------------// SYSCLK_Crystal_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use an 22.1184MHz crystal// as its clock source. Assumes a 22.1184 MHz crystal and associated loading// capacitors are connected at XTAL1 and XTAL2.//void SYSCLK_Crystal_Init (void){ int i; // delay counter char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page SFRPAGE = CONFIG_PAGE; // Set SFR Page

OSCXCN = 0x67; // start external oscillator with // 22.1184MHz crystal (XFCN = 7)

for (i=0; i < 256; i++) ; // XTLVLD blanking interval (>1ms)

while (!(OSCXCN & 0x80)) ; // Wait for crystal osc. to settle

SFRPAGE = LEGACY_PAGE; RSTSRC = 0x04; // enable missing clock detector

SFRPAGE = CONFIG_PAGE; CLKSEL = 0x01; // select external oscillator as SYSCLK // source

OSCICN = 0x00; // disable internal oscillator

SFRPAGE = SFRPAGE_SAVE; // Restore SFR page}

//-----------------------------------------------------------------------------// SYSCLK_C_RC_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use an external RC network// or a single capacitor as its clock source. Assumes an RC network is// connected to XTAL1 or a single capacitor is connected to XTAL1 and// XTAL2.//

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22 Rev. 2.1

void SYSCLK_C_RC_Init (void){ char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page SFRPAGE = CONFIG_PAGE; // Set SFR Page

OSCXCN = 0x47; // start external oscillator in // C/RC mode with XFCN = 7 SFRPAGE = LEGACY_PAGE; RSTSRC = 0x04; // enable missing clock detector

SFRPAGE = CONFIG_PAGE; CLKSEL = 0x01; // select external oscillator as SYSCLK // source

OSCICN = 0x00; // disable internal oscillator

SFRPAGE = SFRPAGE_SAVE; // Restore SFR page}

//-----------------------------------------------------------------------------// SYSCLK_CMOS_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to the external oscillator in// CMOS clock mode. Assumes a CMOS clock generator is connected to XTAL1.//void SYSCLK_CMOS_Init (void){ char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page SFRPAGE = CONFIG_PAGE; // Set SFR Page

OSCXCN = 0x20; // start external oscillator in // CMOS clock mode.

SFRPAGE = LEGACY_PAGE; RSTSRC = 0x04; // enable missing clock detector

SFRPAGE = CONFIG_PAGE; CLKSEL = 0x01; // select external oscillator as SYSCLK // source

OSCICN = 0x00; // disable internal oscillator

SFRPAGE = SFRPAGE_SAVE; // Restore SFR page}

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C8051F12x Example//-----------------------------------------------------------------------------// F12x_Osc_Init.c//-----------------------------------------------------------------------------// Copyright 2003 Cygnal Integrated Products, Inc.//// AUTH: FB// DATE: 27 DEC 02//// This program shows an example of configuring the internal// and external oscillators.//// Target: C8051F12x// Tool chain: KEIL C51 6.03 / KEIL EVAL C51//

//-----------------------------------------------------------------------------// Includes//-----------------------------------------------------------------------------

#include <c8051f120.h> // SFR declarations

//-----------------------------------------------------------------------------// 16-bit SFR Definitions for ‘F12x//-----------------------------------------------------------------------------

sfr16 DP = 0x82; // data pointersfr16 ADC0 = 0xbe; // ADC0 datasfr16 ADC0GT = 0xc4; // ADC0 greater than windowsfr16 ADC0LT = 0xc6; // ADC0 less than windowsfr16 RCAP2 = 0xca; // Timer2 capture/reloadsfr16 RCAP3 = 0xca; // Timer3 capture/reloadsfr16 RCAP4 = 0xca; // Timer4 capture/reloadsfr16 TMR2 = 0xcc; // Timer2sfr16 TMR3 = 0xcc; // Timer3sfr16 TMR4 = 0xcc; // Timer4sfr16 DAC0 = 0xd2; // DAC0 datasfr16 DAC1 = 0xd2; // DAC1 datasfr16 PCA0CP5 = 0xe1; // PCA0 Module 5 capturesfr16 PCA0CP2 = 0xe9; // PCA0 Module 2 capturesfr16 PCA0CP3 = 0xeb; // PCA0 Module 3 capturesfr16 PCA0CP4 = 0xed; // PCA0 Module 4 capturesfr16 PCA0 = 0xf9; // PCA0 countersfr16 PCA0CP0 = 0xfb; // PCA0 Module 0 capturesfr16 PCA0CP1 = 0xfd; // PCA0 Module 1 capture

//-----------------------------------------------------------------------------// Global CONSTANTS//-----------------------------------------------------------------------------

sbit LED = P1^6; // LED=’1’ means ONsbit SW1 = P3^7; // SW1=’0’ means switch pressed

//-----------------------------------------------------------------------------// Function PROTOTYPES//-----------------------------------------------------------------------------

void SYSCLK_IntOsc_Init (void);

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24 Rev. 2.1

void SYSCLK_Crystal_Init (void);void SYSCLK_C_RC_Init (void);void SYSCLK_CMOS_Init (void);

//-----------------------------------------------------------------------------// MAIN Routine//-----------------------------------------------------------------------------

void main (void) {

WDTCN = 0xde; // disable watchdog timer WDTCN = 0xad;

// select one of the following functions to initialze the system clock SYSCLK_IntOsc_Init ();// SYSCLK_Crystal_Init ();// SYSCLK_C_RC_Init ();// SYSCLK_CMOS_Init ();

while (1);}

//-----------------------------------------------------------------------------// Initialization Subroutines//-----------------------------------------------------------------------------//-----------------------------------------------------------------------------// SYSCLK_IntOsc_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use the internal oscillator// at its maximum frequency.//void SYSCLK_IntOsc_Init (void){ char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page SFRPAGE = CONFIG_PAGE; // Set SFR Page

OSCICN = 0x83; // Set internal oscillator to // maximum frequency

CLKSEL = 0x00; // Select internal oscillator as // SYSCLK source

SFRPAGE = SFRPAGE_SAVE; // Restore SFR page}

//-----------------------------------------------------------------------------// SYSCLK_Crystal_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use an 22.1184 MHz crystal// as its clock source. Assumes a 22.1184 MHz crystal and associated loading// capacitors are connected at XTAL1 and XTAL2.//void SYSCLK_Crystal_Init (void){ int i; // delay counter char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page SFRPAGE = CONFIG_PAGE; // Set SFR Page

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OSCXCN = 0x67; // start external oscillator with // 22.1184MHz crystal (XFCN = 7)

for (i=0; i < 256; i++) ; // XTLVLD blanking interval (>1ms)

while (!(OSCXCN & 0x80)) ; // Wait for crystal osc. to settle

SFRPAGE = LEGACY_PAGE; RSTSRC = 0x04; // enable missing clock detector

SFRPAGE = CONFIG_PAGE; CLKSEL = 0x01; // select external oscillator as SYSCLK // source

OSCICN = 0x00; // disable internal oscillator

SFRPAGE = SFRPAGE_SAVE; // Restore SFR page}

//-----------------------------------------------------------------------------// SYSCLK_C_RC_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use an external RC network// or a single capacitor as its clock source. Assumes an RC network is// connected to XTAL1 or a single capacitor is connected to XTAL1 and// XTAL2.//void SYSCLK_C_RC_Init (void){ char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page SFRPAGE = CONFIG_PAGE; // Set SFR Page

OSCXCN = 0x47; // start external oscillator in // C/RC mode with XFCN = 7 SFRPAGE = LEGACY_PAGE; RSTSRC = 0x04; // enable missing clock detector

SFRPAGE = CONFIG_PAGE; CLKSEL = 0x01; // select external oscillator as SYSCLK // source

OSCICN = 0x00; // disable internal oscillator

SFRPAGE = SFRPAGE_SAVE; // Restore SFR page}

//-----------------------------------------------------------------------------// SYSCLK_CMOS_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to the external oscillator in// CMOS clock mode. Assumes a CMOS clock generator is connected to XTAL1.//void SYSCLK_CMOS_Init (void){

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26 Rev. 2.1

char SFRPAGE_SAVE = SFRPAGE; // Save Current SFR page SFRPAGE = CONFIG_PAGE; // Set SFR Page

OSCXCN = 0x20; // start external oscillator in // CMOS clock mode.

SFRPAGE = LEGACY_PAGE; RSTSRC = 0x04; // enable missing clock detector

SFRPAGE = CONFIG_PAGE; CLKSEL = 0x01; // select external oscillator as SYSCLK // source

OSCICN = 0x00; // disable internal oscillator

SFRPAGE = SFRPAGE_SAVE; // Restore SFR page}

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Rev. 2.1 27

C8051F2xx Example//-----------------------------------------------------------------------------// F2xx_Osc_Init.c//-----------------------------------------------------------------------------// Copyright 2003 Cygnal Integrated Products, Inc.//// AUTH: FB// DATE: 27 DEC 02//// This program shows an example of configuring the internal// and external oscillators.//// Target: C8051F2xx// Tool chain: KEIL C51 6.03 / KEIL EVAL C51//

//-----------------------------------------------------------------------------// Includes//-----------------------------------------------------------------------------

#include <c8051f200.h> // SFR declarations

//-----------------------------------------------------------------------------// 16-bit SFR Definitions for ‘F2xx//-----------------------------------------------------------------------------

sfr16 DP = 0x82; // data pointersfr16 ADC0 = 0xbe; // ADC0 datasfr16 ADC0GT = 0xc4; // ADC0 greater than windowsfr16 ADC0LT = 0xc6; // ADC0 less than windowsfr16 RCAP2 = 0xca; // Timer2 capture/reloadsfr16 T2 = 0xcc; // Timer2

//-----------------------------------------------------------------------------// Function PROTOTYPES//-----------------------------------------------------------------------------

void SYSCLK_IntOsc_Init (void);void SYSCLK_Crystal_Init (void);void SYSCLK_C_RC_Init (void);void SYSCLK_CMOS_Init (void);

//-----------------------------------------------------------------------------// MAIN Routine//-----------------------------------------------------------------------------

void main (void) {

WDTCN = 0xde; // disable watchdog timer WDTCN = 0xad;

// select one of the following functions to initialze the system clock SYSCLK_IntOsc_Init ();// SYSCLK_Crystal_Init ();// SYSCLK_C_RC_Init ();// SYSCLK_CMOS_Init ();

while (1);

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28 Rev. 2.1

}

//-----------------------------------------------------------------------------// Initialization Subroutines//-----------------------------------------------------------------------------//-----------------------------------------------------------------------------// SYSCLK_IntOsc_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use the internal oscillator// at its maximum frequency.//void SYSCLK_IntOsc_Init (void){ OSCICN = 0x87; // Set internal oscillator to // maximum frequency and enable missing // clock detector}

//-----------------------------------------------------------------------------// SYSCLK_Crystal_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use an 22.1184 MHz crystal// as its clock source. Assumes a 22.1184 MHz crystal and associated loading// capacitors are connected at XTAL1 and XTAL2.//void SYSCLK_Crystal_Init (void){ int i; // delay counter

OSCXCN = 0x67; // start external oscillator with // 22.1184MHz crystal

for (i=0; i < 256; i++) ; // XTLVLD blanking interval (>1ms)

while (!(OSCXCN & 0x80)) ; // Wait for crystal osc. to settle

OSCICN = 0x88; // select external oscillator as SYSCLK // source and enable missing clock // detector}

//-----------------------------------------------------------------------------// SYSCLK_C_RC_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to use an external RC network// or a single capacitor as its clock source. Assumes an RC network is// connected to XTAL1 or a single capacitor is connected to XTAL1 and// XTAL2.//void SYSCLK_C_RC_Init (void){ OSCXCN = 0x47; // start external oscillator in // C/RC mode with XFCN = 7

OSCICN = 0x88; // select external oscillator as SYSCLK // source and enable missing clock

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// detector}

//-----------------------------------------------------------------------------// SYSCLK_CMOS_Init//-----------------------------------------------------------------------------//// This routine initializes the system clock to the external oscillator in// CMOS clock mode. Assumes a CMOS clock generator is connected to XTAL1.//void SYSCLK_CMOS_Init (void){ OSCXCN = 0x20; // start external oscillator in // CMOS clock mode.

OSCICN = 0x88; // select external oscillator as SYSCLK // source and enable missing clock // detector}

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