IT 212-2

1. IT 212-2 Part 5 Chapters 15-16

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. How an Uninterruptible Power Supply Works • Two types • Offline • Online

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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