arm microcontroller interfacing tutorial -...

MicrocontrollerInterfacingCSE/EE5/7385MicrocontrollerArchitectureandInterfacing

DavidHoungninou

SouthernMethodistUniversity

Tableofcontent

1. Targetdevice:MCBSTM32C

2. References

3. GPIOports:registersandpins

4. InterfacingwiththeLEDs

2

Targetdevice:MCBSTM32C

• 72MHzARMCortex™-M3

• On-ChipFlash:256KB• On-ChipRAM:64KB

• ExternalMemory:8KBI2CFlash

• Serial/UARTPort• 80GPIOpins

3

Targetdevice:MCBSTM32C

• 72MHzARMCortex™-M3

• On-ChipFlash:256KB• On-ChipRAM:64KB

• ExternalMemory:8KBI2CFlash

• Serial/UARTPort• 80GPIOpins

4

Usefulreferences

• Evaluationboard:MCBSTM32C

• Microcontroller:STM32F107VC

• Manufacturer:STMicroelectronics

• Boarddocumentation:www.keil.com/dd/chip/4889.htm

• Boardschematic:

www.keil.com/mcbstm32c/mcbstm32c-base-board-schematics.pdf

• MicrocontrollerReferencemanual:RM0008davidkebo.com/documents/RM0008_Reference_manual.pdf

5

WhatisaGPIOport?

• AGPIOportisagroupofuser-configurablepinsforGeneralPurposeInput/Output• TheSTM32F107VChas7generalpurposeinput/output(GPIO)ports

• The7GPIOPortsareA,B,C,D,E,FandG.• Eachportcanhaveupto16pins• Eachporthas7registers

6

WhatisaGPIOport?

7

WhatisaGPIOpin?

A GPIO pin is a generic pincontrollable by the user atrun time and configurableto be input or output.

Input

Output

8

WhatisaGPIOregister?

AGPIO registerisa32-bit storagearea thatholdconfigurationbitsforaGPIOpin

Exampleofaconfigurable32-bit register

9

7GPIOportregisters(32-bit)

• ConfigurationregisterlowGPIOx_CRL• ConfigurationregisterhighGPIOx_CRH• InputdataregisterGPIOx_IDR• OutputdataregisterGPIOx_ODR• Set/resetregisterGPIOx_BSRR• ResetregisterGPIOx_BRR• LockingregisterGPIOx_LCKR

the'x' istheportname.e.g.GPIOA_IDRistheinputdataregisterassociatedwithportA.

(Reference:RM0008Page170)

10

Tutorial:InterfacingwiththeLEDs

• WriteaprogramthatinterfaceswiththeLEDs

• Togglethe08LEDsON/OFF• ThetogglespeedoftheLEDsshoulddependontheinputvoltageoftheADC1input.

11

InterfacingwiththeLEDs

Steps1. Initializethemicrocontroller

2. EnabletheclockfortheLEDs

3. SetuptheGPIOfortheLEDs

4. SetupandinitializetheADC

5. ReadtheADCvalues

6. BlinktheLEDs

12

Initializethemicrocontroller

SystemInit()isafunctiondefinedinthesourcefilesystem_stm32f10x_cl.c

Thepurposeofthisfunctionisto:

• Initializetheembeddedflashinterface

• Updatethesystemclockfrequency

13

EnabletheclockfortheLEDs

• TheARMmicrocontrollerdoesnotholdtheclockactivecontinuously

• EnabletheclockfortheLEDsmanually(PortE)• Setconfigurationbit(s)inregisterRCC_APB2ENR• RCC_APB2ENR:AdvancedPeripheralBus2EnableRegister

RCC->APB2ENR|=1<<6; //EnableGPIOEclock14

SetuptheGPIOfortheLEDs

• LEDspinsarewiredtoGPIOE(PortE)• The16pinsarePE0toPE15• LEDsarewiredtopinsPE8,…PE15• Configurethepinsasoutput

GPIOE->CRH=0x33333333;

15

SetuptheGPIOfortheLEDsName r/w Bits Function

GPIOx_CRL Portconfigurationregisterlow rw CNF[1:0],MODE[1:0] Configurelowest8bitofport x.INorOUT

GPIOx_CRH Portconfigurationregisterhigh rw CNF[1:0],MODE[1:0] Configurehighest8bitofport x.INorOUT

GPIOx_IDR portinputdataregister r IDR[15:0]Readstateofpinsconfiguredforinputonport x (Lowest16bitsofword)

GPIOx_ODR portoutputdataregister rw ODR[15:0]WritetopinsconfiguredforOutputonport x (Lowest16bitsofword)

GPIOx_BSRR Portbitset/resetregister w BS[15:0],BR[15:0]AtomicSet/ResetindividualPinsconfiguredforOutput.

GPIOx_BRR Portbitresetregister w BR[15:0]AtomicResetindividualPinsconfiguredforOutput.(Lowest16bitsofword)

GPIOx_LCKR Portconfigurationlockregister rw LCK[15:0],LCKKLockindividualpinsofport x (FreezeCRLandCRHofports)

Table1:GPIOConfigurationRegisters16

SetuptheGPIOfortheLEDsConfigurationmode CNF1 CNF0 MODE1 MODE0 PxODRregister

GeneralPurposeOutput

Push-Pull0

0

011011

0or1

OpenDrain 1 0or1

AlternatefunctionOutput

Push-Pull1

0 Don'tCare

OpenDrain 1 Don'tCare

Input

Analog0

0

00

Don'tCare

Floating 1 Don'tCare

Pull-Down1 0

0

Pull-Up 1

Portconfigurationregistertopins Table2:Portbitconfigurationsummary 17


Portconfigurationregisterlow(GPIOx_CRL)(x=A..G)

Portconfigurationregisterhigh(GPIOx_CRH)(x=A..G)

18


• GPIOE_CRH(ControlRegisterHigh)controlsbits8through15.

• ConfigureGPIOE_CRHasa pushpulloutput (Seetable2)

CNFx[1:0]=00andMODEx[1:0]=01,10or11

Registerbitpattern:0011 0011 0011 0011 0011 0011 0011 0011

GPIOE->CRH=0x33333333;

19

SetupandinitializetheADC

TheAnalogtoDigitalConverter(ADC)convertsananaloginputtoadigitalinput.

ADCtoSTM32F107VCtoDAC

20


EnabletheclockfortheADC.

RCC->APB2ENR|=1 <<9;

APB2peripheralclockenableregister(RCC_APB2ENR)

21


• ThepotentiometerconnectstoportpinPC4(ADC12_IN14)

• PinPC4mustbeconfiguredasananaloginput.(Seetable2)

• Pin4isconnectedtoCRL(Configurationregisterlow)ToconfigurePC4weusethefollowingmask:

1111 1111 1111 0000 1111 1111 1111 1111

AbitwiseANDofGPIOC->CRLandthemaskclearsCNF4andMODE4

GPIOC->CRL&=0xFFF0FFFF;

22

SetuptheADC

Portconfigurationregisterlow(GPIOx_CRL)(x=A..G)

Portconfigurationregisterhigh(GPIOx_CRH)(x=A..G)

23

ADCSequenceregisters

TheSTM32F107has18analoginputchannels.

Sequenceregistersconfigurethenumberofchannelstosample

24


Bits23:20L[3:0]:Regularchannelsequencelength.Numberofconversionsintheregularchannelconversionsequence.

0000:1conversion,0001:2conversions,...1111:16conversionsBits19:15SQ16[4:0]:16thconversioninregularsequence.Channelnumberassignedasthe16thintheconversionsequence.

Bits14:10SQ15[4:0]:15thconversioninregularsequence

25


TheSTM32F107has18analoginputchannels.Thepotentiometeriswiredtochannel14Forasingleconversion:ADC1->SQR1=0x00000000;//RegularchannelsingleconversionADC1->SQR2=0x00000000;//Clear register

ADC1->SQR3=(14<<0); //channel14as1stconversion

26

ADCsampletimeregistersADC_SMPR

ThenumberofADC_CLKcyclesthattheADCsamplestheinputvoltageismodifiedusing:

SMP[2:0]bitsintheADC_SMPR1andADC_SMPR2registers

27

ADCsampletimeregisterADC_SMPR

Bits23:0SMPx[2:0]:ChannelxSampletimeselection

Selectthesampletimeindividuallyforeachchannel.

28

000:1.5cycles 001:7.5cycles 010:13.5cycles 011:28.5cycles

100:41.5cycles 101:55.5cycles 110:71.5cycles 111:239.5cycles

Table3:ADCsampletimeconfiguration


29

TheADCshoulddelayreadingfor5.15uS

ForanADCCLKrunningat14MHz

Determinethesampletime(SettingforSMPx)?


30

TheADCshoulddelayreadingfor5.15uS

ForanADCCLKrunningat14MHz

Determinethesampletime(SettingforSMPx)?

T=1/14MHz

T=0.07142uS

#of cycles =5.15uS /T=5.15uS /0.07142uS

#of cycles =72

ADCSampleTimeBitsRegister

Setchannel14atasampletimeof72cycles:

Thebitconfigurationfor72cyclesis110(Table3)

ADC1->SMPR1=6<<12;

ADC1->SMPR2=0x00000000;//Clearregister

31

ADCControlRegisters(ADC_CR)

32

TheADCiscontrolledusingtwocontrolregistersADC_CR1 andADC_CR2Bit8SCAN(Scanmode):Inthismode,theinputsselectedthroughADC_SQRxregistersareconverted.

Bit5EOCIE (InterruptenableforEOC): enable/disabletheEndofConversioninterrupt.

ADCblockdiagram(page216)RM0008

ADCControlRegisters(ADC_CR1)

33

Tointerruptthemicrocontrollerattheendofconversion:

ADC1->CR1|=(1<<5); //EOCinterrupt

NIVC->ISER[0]|=(1<<18); //Interruptnumber18


34

SWSTART: Startconversionofregularchannels

EXTTRIG: Enableexternalsignal

EXTSEL SWSTARTastrigger.

ALIGN: Dataalignment.0:rightalignment, 1:leftalignment

RSTCAL: Resetcalibration

CAL: A/DCalibration

CONT: Continuousconversion

ADON: A/DconverterON/OFF


35

Configuration

ADC1->CR2|=(7<<17); //SetSWSTARTastrigger

ADC1->CR2|=(1<<20); //Enableexternaltrigger

ADC1->CR2&=~(1<<11); // Rightdata alignment

ADC1->CR2|=(1<<1); // Continuousconversion

ADC1->CR2|=(1<<0); //TurnADCON


Enableexternaltrigger,EXTSEL=SWSTART,Continuousconversion,ADCenable

ADC1->CR2=(1 <<20)|(7<<17)| (1 <<1) |(1<<0);

36


37

CalibrationADC1->CR2|=(1<<3); //resetcalibration

while(ADC1->CR2&(1<<3)); //waituntilresetfinished

ADC1->CR2|=(1<<2); //startcalibration

while(ADC1->CR2&(1<<2)); //waituntilcalibrationfinished

ConversionADC1->CR2|=(1<<22); //start SWconversion

ADCStatusandDataRegisters(ADC_SR)

38

Bit4STRT RegularchannelStartflag

Bit3JSTRT InjectedchannelStartflag

Bit2JEOC Injectedchannelendofconversion

Bit1EOC Endofconversion

Bit0AWD Analogwatchdogflag

ADCStatusandDataRegisters(ADC_DR)

39

Bits31:16ADC2DATA[15:0] ContaintheregulardataofADC2.

Bits15:0DATA[15:0] Containtheconversionresultfromtheregularchannels.

ADCStatusandDataRegisters(ADC_SR/ADC_DR)

if (ADC1->SR&(1 <<1)){//Ifconversionhasfinished(CheckEOCbit)

AD_val =ADC1->DR&0x0FFF;//ReadADconvertedvalue

ADC1->CR2|=1 <<22;//Startnewconversion

}

40

BlinktheLEDs(Read-modify-writemethod)

const long led_mask[] = {1<<15, 1<<14, 1<<13, 1<<12, 1<<11, 1<<10, 1<<9, 1<<8};GPIOE->ODR|=led_mask[num]; /*Turn LEDnum on*/

for (i = 0; i < ((AD_val << 8) + 100000); i++); /*ADCdelay*/

GPIOE->ODR&=~led_mask[num]; /*Turn LEDnum off*/

41

BlinktheLEDs(Read-modify-writemethod)

42

GPIOE->ODR|=led_mask[num]; /*Turn LEDnum on*/

Portoutputdataregister(GPIOx_ODR)(x=A..G)

BlinktheLEDs(Atomicmethod)

const long led_mask[] = {1<<15, 1<<14, 1<<13, 1<<12, 1<<11, 1<<10, 1<<9, 1<<8};

GPIOE->BSRR=led_mask[num]; /*Turn LEDnum on*/

for (i = 0; i < ((AD_val << 8) + 100000); i++); /*ADCdelay*/GPIOE->BSRR=led_mask[num] << 16; /*Turn LEDnum off*/

43

BlinktheLEDs(Atomicmethod)

SetBits

ResetBits

Note:Shiftingby16bitsgoesfromSet bitstoReset bits

44

Timers

Timersareclocksourcesusedasthe‘heartbeats’foroperations.

e.g.ofapplicationsusingtimers:• Countingpulses• Measuringtimeperiodsofwaveforms

• Generatingpulsewidthmodulation(PWM)signals

• Triggeringexternaldevices• Timingspecialevents

45

Timers

03groupsoftimers:

• BasicTimers

• GeneralPurposeTimers

• AdvancedTimers (TIM1&TIM8)

46

Basictimers

TIM6,TIM7

Applications:noI/Ochannelsforinputcapture

noPWMgeneration

Onlyusedfortime-basegeneration

47

GeneralPurposeTimers

TIM2,TIM3,TIM4,TIM5

Applications:• PWMgeneration

• Inputcapture• Time-basegeneration

• Outputcompare

48

Advancedtimers

TIM1,TIM8

Applications:• AdvancedPWMgeneration

• Inputcapture• Time-basegeneration

• Outputcompare

49

Timerspin

EachtimerisassociatedwithanI/Opin

Configurethealternatefunctiontousethetimerpin

Whatisanalternatefunction?InadditiontogeneralpurposeinputandoutputtheARMsubsystemcanimplementotherspecializedinputoutputfunctions.

e.g.TIM4_Ch4 isanalternatefunctionforpinPB9

50

TIMx functionaldescription

Themainblockofthetimerisa16-bitcounterTIMx_CNT withanauto-reloadregister TIMx_ARRThecountercancountup,downorbothupanddown.

Thecounterclockcanbedividedbyapre-scalerTIMx_PSC

51General-purposetimers(TIM2toTIM5)RM0008Manual15.1Page364


Countertimingdiagramwithpre-scalerdivisionchangefrom1to2

52


Countertimingdiagramwithpre-scalerdivisionchangefrom1to4

53

Timerconfiguration

54

Steps:

1. Enableclocktothetimer2. EnabletheAlternatefunction

andtheGPIOclock3. Settheinternal clockas

systemclock4. Setthepre-scaler5. Enablethetimer

Registers

RCC->APB1ENRRCC->APB2ENR

(TIMx_SMCR)TIMx slavemodecontrolregister

(TIMx_PSC)TIMx pre-scalerregister(TIMx_CR1)TIMx controlregister

Timerconfiguration

55

Steps:

1. Enableclocktothetimer2. EnabletheAlternatefunction

andtheGPIOclock3. Settheinternal clockas

systemclock4. Setthepre-scaler5. Enablethetimer

Notes abouttheclockusage:

TheHSI clocksignalisgeneratedfromaninternal8MHzRCoscillatorandcanbeuseddirectlyasasystemclock.(HSI)high-speedinternaloscillator

Tosetthepre-scalerregister:Usethecounterclockfrequency(CK_CNT)CK_CNT=fCK_PSC /(PSC[15:0]+1)

Timerexample

Adeveloperiswritingafunctionforacounteruseratimer.

TheinternalHISclocksignalrunsat8MHzWhatisvaluetosetthepre-scalertocounteverymillisecond?

CK_CNT=fCK_PSC /(PSC[15:0]+1)

PSC[15:0]+1=fCK_PSC /1000

PSC[15:0]=(fCK_PSC /1000)– 1

PSC[15:0]=7999

56

Timerclock

57

e.g:TouseTIM4

RCC->APB1ENR|=(1<<2); //enableclocktoTIM4.

AdvancedPeripheralBus1EnableRegister

Timerclock

58

e.g:TouseTIM4

RCC->APB2ENR|=(1)|(1<<3); //EnabletheA.FclockandtheGPIOclock

Advanced Peripheral Bus 2 Enable Register

Timerpre-scalerregister

59

TIM1&TIM8pre-scaler(TIMx_PSC)PSC[15:0]:Pre-scalervalue

Timerslavemoderegister

60

TIM1&TIM8slavemodecontrolregister(TIMx_SMCR)SMS=000,thepre-scalerisclockeddirectlybytheinternalclock.

Timercontrolregister

61

TIM1&TIM8controlregister1(TIMx_CR1)CEN:Counterenable0:Counterdisabled1:Counterenabled

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