IT 212-2

Part 5Chapters 15-16

How Energy Turns Into Data

• Perceptions are analog – one continuous wavy line of events moving at predictable rates

• But really – things are more digital – discrete separate events with different numerical values

• Digital to Analog Converters [DACs] and Analog to Digital Converters [ADCs] handle all conversions to and from each form of data

• Charged-Coupled Devices turn light into electrical energy

• Light is turned into electrical energy

Analog and Digital Converters

• Visible light and audible sound both travel in waves – The brighter the light, the more electrical current it

can be converted into– The louder the sound, the more electrical current it

can be converted into

• Computers convert all analog input into digital values it can use

• The opposite conversion must also take place upon sending digital data to output devices

Analog Converters

• Analog to Digital Converters constantly samples an analog signal sent to it in the form of a wavering current

• Each time the current is measured, it is assigned a number that represents its value at the moment it was recorded

• Usually used for collecting input in the form of sound or light

Digital Converters

• Digital to Analog converters changes a string of digital values into rapidly changing voltages

• Current is sent along different patterns through resistors resulting in an analog stream of current that is varies to correspond to digital data

• Usually used for output

Digital and Analog Conversion

• Precision is affected by how often the analog signal is sampled– More samples detect finer changes in the

signal

• Precision is also affected by the sensitivity of the sensors

Digital and Analog Conversion

• Resolution with respect to DAC and ADC is the range of values and amount of information that a device can hold for one sample– Resolution depends on the bits a device can

devote to a digital translation of the analog values

Digital and Analog Conversion

• If a DAC has only one bit to represent a sample of an analog signal it can only show whether the analog signal is on or off, black or white

• If a DAC has 16 bits to express each digital sample it can represent 256 shades of red– Higher the number resolution number, the

higher the definition in either sound or color

How Scanners and Digital Cameras See

• Scanners and digital cameras have to convert different amounts of light into corresponding energy levels, and eventually 1s & 0s

• Both use a charge-coupled device [CCDs] to solve the problem– A camera must divide light passing through the lens

into green, red, and blue elements– It must also register the light that falls at the same

moment on a very small area – the size of 2 postage stamps

How a Scanner Sees• CCDs consist of rows of photodiodes connected like

beads on a string

• When exposed to a varied light path, each photodiode converts the amount of light it receives into a corresponding voltage

• After the microscopic instant the diodes register the amount of light each receives, the charge is passed off to a circuit leading to an ADC chip

• Instantly the charges in the string of diodes move to the diodes next to them in the direction of the ADC

How a Digital Camera Sees

• Inside of a digital camera a CCD array is used to capture a two dimensional area struck by light

• The array consists of strips of CCDs– Covering the array are colored filters that

pick up only red, blue or green light– Each strip of red, blue, and green diodes are

coupled as they were in the scanner• This groups all of the same colors together

How a Digital Camera Sees

• At the bottom of the array the CCDs lead to a circuit where each of the streams of analog voltage stream into an ADC

• This process continues until all the values are converted into numerical values

• The ADC turn the digital data into a color value for each photo diode in the CCD array

How an Uninterruptible Power Supply Works

• Two types– Offline– Online

How an Offline Uninterruptible Power Supply

Works• Offline or passive UPSs split incoming current

into two branches– One feeds the normal power of the PC– The other passes through a battery charger which

changes the current from AC to DC to keep the battery charged

• If power fails, within 4-20 milliseconds the microprocessor inside the the UPS closes a switch that sends DC through an inverter and turns the battery’s DC current into AC needed by the PC

How an Online Uninterruptible Power Supply

Works• Online or serial UPSs feed all current

through an AC-DC converter, from there to a battery, then to an inverter and then to the PC– This way, the UPSs battery is always

charged and supplying current to the PC

• If power fails, a microswitch breaks the connection between the wall and the UPS and current flows from the battery

How Surge Protectors Work

• Since we know power has noise and that it flows in irregular currents – we need to protect PCs as much as possible from this– Some devices are very sensitive to small

fluctuations in electricity and are damaged easily

How Surge Protectors Work

• Power Surge– A sudden spike in voltage

• First line of defense is shunt mode– Uses a metal oxide varistor [MOV] between the power line and its

ground line

• MOVs only carry current if voltages reach a certain level – surge protectors usually contain multiple MOVs for redundancy

• If a surge is too large, it is sent to a thermal fuse to block the current– Melts if too hot and stops current from flowing

through the lines

How Surge Protectors Work

• Basic line conditioning– Contained by a toroidal choke coil – Compensation for the irregularities of

current supplied from electrical sources

• Current on the way to the PC passes through the coil – Fluctuations in the current create another

current in the coil’s wire, which creates a magnetic field that opposes noise and smoothes out the current

Expansion Cards

• Types– 8 Bit Expansion Card– 16 Bit – or ISA Card– 32 Bit MCA Card– 32 Bit EISA Card– 32 Bit Local Bus Card– 32 Bit Accelerated Graphics Port

8 Bit Expansion Card

• Original type of expansion card in the IBM PC

• Had 31 pairs of connectors that plugged into the motherboard– Did not even use all of them

16 Bit or ISA Card

• Industry Standard Architecture

• 18 more pairs of connectors than the original 8 bit cards

• Transmits data over 16 data lines– Doubled the amount of data compared to an

8 bit card

32 Bit MCA Card

• Micro Channel Architecture– Uses 32 of 93 lines to send and receive data

• Uses special technology that like plug and play made it easier to install

• IBM refused to let others clone this card for a long time after introducing it

32 Bit EISA Card

• Extended Industry Standard Architecture

• First card designed to use all 97 of the slot’s connectors

• Transmits 32 bits of data• EISA slots will also accept 8 bit and 16

bit cards unlike 32 bit MCA card

32 Bit PCI Local Bus Card

• Peripheral Component Interconnect• Connectors similar to MCA and EISA

cards• Handles all 32 bits of data at a time• Smaller and more compact than ISA

cards• Won’t accept ISA or 8 bit cards• Currently the most prevalent in PCs

32 Bit Accelerated Graphics Port

• Known as AGP ‘slots’

• Designed for only a specific type of video card

• 44 pins – or – connectors on an AGP card

How AGP Works

• AGP chipset replaces the PCI bus’ input/output controller

• Coupled with a Pentium 4 chip and RDRAM memory capable of 3.2GB/sec data transfer

• Handles transfers of data among memory, CPU and the ISA controller – all simultaneously

• Also handles transfers to the PCI local bus at 132MB/sec

How AGP Works

• The AGP chipset puts the AGP port on the same part of the bus as memory, with data transfers of up to 1056MB/sec between those items

• The arrangement allows AGP accelerated graphics adapter to replace the adapter on the PCI bus– Eliminates the need for video RAM

• Provides faster Direct Memory Access enabling some to read/write to memory without the help of the CPU

• Sends four bursts of 32 bits of data with every clock tick equaling 1056MB/sec data transfer to and from RAM

PCI Local Bus

• Signals from the CPU go through a I/O for PCI local bus operations

• PCI controller examines all signals to determine where the intended address is – either for the local bus or non-local bus adapter

• Routes all signals meant for a non-local bus adapter to a second controller – usually the ISA controller– Moves bits at 16 bits at a time for ISA circuits– 32 bits at a time for EISA or MCA circuits

PCI Local Bus

• Routes all signals sent to the local bus at 32 bits at a time

• Data on this path travels at 33, 100, or 133MHz depending on when the motherboard was manufactured