Pci,usb,scsi bus

PCI,SCSI and USB bus details

1. PCI, USB, SCSI

2. PCI PCI (Peripheral Component Interconnect) Developed by Intel(1993) Used for interfacing processor with its chipset Very successful, widely used Much faster than ISA(Industry Standard Architecture)

3. Features of PCI Bus Synchronous Bus Architecture. 64 Bit Addressing. Linear Burst Mode Data Transfer. Large Bandwidth. PCI operates at 66MHz and at 33MHz. Plug-and-Play(PnP).

4. USB The very well known connection port available on your PC is the USB port. USB is an acronym for Universal Serial Bus The change that has been caused by this standard and its wide application is definitely mentionable. USB was created by a core group of companies that consisted of Compaq, Digital, IBM, Intel, Northern Telecom and Microsoft.

5. Features of USB A maximum of 127 peripherals can be connected to a single USB host controller. USB device has a maximum speed up to 480 Mbps (for USB 2.0). Length of individual USB cable can reach up to 5 meters without a hub and 40 meters with hub. USB acts as "plug and play" device. USB can draw power by its own supply or from a computer. USB devices use power up to 5 voltages and deliver up to up to 500 mA . If a computer turns into power-saving mode, some USB devices will automatically convert themselves into "sleep" mode.

6. Applications of USB USB connections are used to connect computer peripherals such as mouse, keyboards, digital cameras, printers, flash drives, joysticks, scanners, modems, storage devices, etc. It has become common on other devices such as phones, PDAs, etc.

7. SCSI S mall C omputer S ystems I nterface Developed by Shugart Associates (1981) Originally called S hugart A ssociates S ystems I nterface (SASI) Set of standards for physically connecting and transferring data between computers and peripheral devices SCSI ports allows data to be transmitted in a “daisy chain” Up to 8 or 16 devices can be attached on a single SCSI bus. SCSI uses handshaking signal between devices

8. SCSI Bus

9. SCSI Bus P hases

10. Bus Free Phase   In a busy system, the SCSI bus may be free for as little as 1.2 ps while there is no device requesting the bus . if the bus is free it could remain free indefinitely. Arbitration Phase A device can arbitrate and be granted the bus in 3.6 ps or less. Devices that lose arbitration can try again when the bus is in free state. Selection Phase The selection phase can select the target in 580 ns. If the target does not respond the bus waits for 250 ms and then enters the free phase.        Message Phase The message phase is the first information transfer phase in the connection, which allows the initiator to send an Identification message to the target. In SCSI messages are always transferred asynchronously. Command Phase   The target responds to the Inquiry data, during the command phase Data In Phase   The data transfer can be done synchronously if both the initiator and the target have previously established a synchronous data transfer agreement.        Status The target finally sends a single status byte asynchronously during status phase .        Message In Phase The last information that is transferred in the established connection is typically the command complete message during the message in phase. Bus Free Phase The target device releases the BSY signal and returns to the Bus Free phase. The bus is now available.         

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