AM53C96 datasheet(30/63 Pages) AMD

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P R E L I M I N A R Y

AMD

Am53C94/Am53C96

FTMREG – Bit 1 – FIM – Forced Initiator Mode

The FIM bit when set forces the device into the initiator

mode. The device will then execute all initiator com-

mands irrespective of the SCSI bus status.

FTMREG – Bit 0 – FTM – Forced Target Mode

The FTM bit when set forces the device into the target

mode. The device will then execute all target commands

irrespective of the SCSI bus status.

Control Register Two (0BH) Read/Write

Control Register Two

CNTLREG2

Address: 0BH

Type: Read/Write

76543

210

DAE

LSP

SBO

TSDR

S2FE

ACDPE

PGRP

PGDP

0000

000

Latch SCSI Phase

Select Byte Order

Tri–State DMA Request

SCSI–2 Features Enable

Abort on Command/Data Parity Error

Pass Through/Generate Register Parity

Pass Through/Generate Data Parity

Data Alignment Enable

16506C-31

The Control Register 2 (CNTLREG2) sets up the device

with various operating parameters.

CNTLREG2 – Bit 7 – DAE – Data Alignment Enable

The DAE bit is used in the initiator Synchronous Data-In

phase only. When the DAE bit is set one byte is reserved

at the end of the FIFO when the phase changes to the

Synchronous Data-In phase. The contents of this byte

will become the lower byte of the DMA word (16-bit)

transfer to the memory, the upper byte being the first

byte of the first word received from the SCSI bus.

Note:

If an interrupt is received for a misaligned boundary on a

phase change to synchronous data the following recov-

ery procedure may be followed. The host processor

should copy the byte at the start address in the host

memory to the Data Alignment Register 0FH (DALREG)

and then issue an information transfer command. The

first word the device will write to the memory (via DMA)

will consists of the lower byte from the DALREG and the

upper byte from the first byte received from the SCSI

bus.

The DAE bit must be set before the phase changes to

the Synchronous Data-In. The DAE bit is reset to zero by

a hard or soft reset or by writing the DALREG when in-

terrupted in the Synchronous Data-In phase.

CNTLREG2 – Bit 6 – LSP – Latch SCSI Phase

The LSP bit is used to enable or disable the latching of

the SCSI phase bits (MSG, C/D and I/O) in the Status

When the LSP bit is set the phase bits STSTREG – Bits

2:0 are latched at the end of each command. This simpli-

fies software for stacked commands. When the LSP bit

is reset the phase bits STATREG – Bits 2:0 reflect the

actual state of the SCSI phase lines at any instant of

time. The LSP bit is reset by a hard or soft reset.

CNTLREG2 – Bit 5 – SBO – Select Byte Order

The SBO bit is used only when the BUSMD 1:0 = 10 to

enable or disable the byte control on the DMA interface.

When SBO is set and the BUSMD 1:0 = 10, the byte con-

trol inputs BHE and AS0 control the byte positions.

When SBO is reset the byte control inputs BHE and AS0

are ignored.

CNTLREG2 – Bit 4 – TSDR – Tri-State DMA

Request

The TSDR bit when set sends the DREQ output signal to

high impedance state and the device ignores all activity

on the DMA request (DREQ) input. This is useful for

wiring-OR several devices that share a common DMA

request line. When the TSDR bit is reset the DREQ

output is driven to TTL levels.

CNTLREG2 – Bit 3 – S2FE – SCSI–2 Features

Enable

The S2FE bit allows the device to recognize two SCSI-2

features. The two features are extended message fea-

ture and the Group 2 command recognition.

Extended Message Feature: When the S2FE bit is set

and the device is selected with attention, the device will

monitor the

ATN signal at the end of the first message

byte. If the

ATN signal is active, the device will request

two more message bytes before switching to the com-

mand phase. If the

ATN signal is inactive the device will

switch to the command phase. When the S2FE bit is re-

set the device as a target will request a single message

byte. As an initiator, the device will abort the selection

sequence if the target does not switch to the command

phase after receiving a single message byte.

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