Compaq 850 manual Functional Description, PCI Scsi

Appendix K Compaq PCI 10/100 Ethernet Adapter

L.2 FUNCTIONAL DESCRIPTION

A block diagram of the SCSI Adapter is shown in Figure L-2. The adapter’s architecture is based on the AIC-7892 SCSI controller working off the 32-bit, 66-/33-MHz PCI bus. Providing full bus mastering capability, the adapter supports data transfers up to 266 MB/s using the burst mode rate on a 66-MHz 32-bit PCI bus. The AIC-7892 controller is an Ultra160 controller with an on-board 20-MIPS SCSI sequencer that can process SCSI commands without intervention from the host microprocessor. The sequencer uses micro-code that is downloaded from the host during initialization. Single-ended SCSI drivers are built into the controller and a 1-K data FIFO and an internal 4-KB SRAM memory. An LED is provided to indicate SCSI bus activity.

The AIC7892 provides a memory interface that is used by the Serial EEPROM and the BIOS ROM. The serial EEPROM stores non-volatile configuration data and the BIOS ROM (which is a flash ROM) contains additional configuration data and SCSI functions. The programmable array logic (PAL) controls the Serial EEPROM-to-AIC7892 interface.

		SCSI
	PAL	Activity
	Chip
Serial
EEPROM
PCI Bus		AIC7892
PCI
		SCSI
Slot
	Controller
BIOS
ROM

	Active Ultra160
		SE Term.
40-MHz
Clock
AIC3860			Int. SCSI Connector (SE)
Transceiver
			Ext. SCSI Connector (SE)
Chip
			Int. SCSI Connector (SE/LVD)

Active Ultra160

SE/LVD Term.

Figure L–2.Compaq/Adaptec Ultra SCSI Adapter Card Block Diagram

The AIC7892 controller supports dual-mode low-voltage differential (LVD) SCSI I/O up to the Ultra160 data rate of 160 Mbytes. Both single-ended (SE) and LVD devices can co-exist on the SCSI bus, although operation will default to the SE mode. In SE mode, transfer rates are limited to the speed of the slower device. High-voltage differential (HVD) devices are supported for rates up to Ultra speeds.

The AIC7892 also supports cyclic redundancy check (CRC) codes, an improvement over parity checking used earlier.

L-2Compaq Personal Computers

Original - December 2000