Figure E-2. Adaptec Aha-2940U U; E.2 Functional Description - Compaq EN Series Technical Reference Manual

Appendix E Wide Ultra SCSI Host Adapter Card
E.2 FUNCTIONAL DESCRIPTION
A block diagram of the Wide Ultra SCSI Card is shown in Figure E-2. The card's architecture is
based on the AIC-7880 SCSI controller. The AIC-7880 controller includes an on-board 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 256-byte FIFO in the data path allowing up
to 15-byte synchronous offsets. An LED is provided to indicate SCSI bus activity.
The AIC 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-AIC7880 interface.
SCSI operations include the processing of 32-byte SCSI command blocks (SCBs). The AIC-7880
can execute up to 254 SCBs by swapping the blocks in and out of 8-KB of system memory as
there is no on-board memory. The SCBs can be handled on the byte level or as an entire block.
BIOS
ROM
Mem. I/F
Serial
EEPROM
Figure E–2. Adaptec AHA-2940U Ultra SCSI Adapter Card Block Diagram
E-2 Compaq Personal Computers
SCSI
Activity
PAL
AIC7880
SCSI
Controller
PCI Bus
Original – April 1998
40-MHz
Clock
Ultra SCSI Connector (Ext)
Wide Ultra SCSI Connector (Int. & Ext.)