Expansion Board Id Registers - Adaptec AHA-1740A Technical Reference Manual

EISA-to-Fast SCSI Host Adapter
resources such as interrupt levels and DMA channels when they are assigned. Refer
to the EISA Specification, Section 2.6 and Section 3.3 for more information.
There are five groups of addressable hardware used to interface the host adapter
with the host system across the EISA bus:
Board ID registers
Configuration registers
BIOS EPROM
Standard Mode (Group 1) I/O ports (used in Standard Mode)
Enhanced Mode (Group 2) I/O ports (used in Enhanced Mode)
Only the Board ID and Configuration registers are accessible after a power on reset
(RESDRV). The I/O port Standard Mode (Group 1) registers are accessible when the
CDEN bit on the board is set. The BIOS EPROM is accessible when both the CDEN
and BIOSEN bits are set.
The board IDs are required for EISA board configuration. The ID is used by the sys-
tem ROM at power up initialization to locate the adapter and determine the slot in
which it is installed. After the RESDRV signal indicates power on, HID0 is set to 7Xh
to indicate not ready. The IDs are loaded by the local processor. The interrupt level,
I/O port base address, BIOS base address, and SCSI initialization parameters are
programmed in the Configuration registers. All of these registers may be written or
read at any time.

Expansion Board ID Registers

The expansion board identifier registers are always available for access on the bus by
the host system. They are used to transfer basic information on the identity of the
board and its revision level from the AHA-1740A/1742A/1744 to the host.
Host ID 0 (HID0, zC80, R)
HID0 is the first byte of the expansion board ID. It is written by the local processor
and read by the system processor. HID0 is initialized to 7Xh on RESDRV. HARDST
or SOFTRST has no effect.
Bit Definition
7 Reserved (0).
6-2 First compressed character of a manufacturer's ID. Bit 6 is the most significant bit.
This character is always "A" wihch results in a compressed code of '00001'B.
1-0 Most significant two bits of the second compressed character of manufacturer's ID.
Bit 1 is the most significant bit. The character is continued in register HID1. The
character is always "D," which is represented by '00100'B.
Hardware Functional Description
4-11