(SET TARGET or CLEAR TARGET). When this bit is set, the chip is a target device by default. When this bit is cleared, the LSI53C875A is an initiator device by default.

Caution: Writing this bit while not connected may cause the loss of a selection or reselection due to the changing of target or initiator modes.

Register: 0x01

SCSI Control One (SCNTL1)

Read/Write

7

6

5

4

3

 

2

1

 

0

EXC

ADB

 

DHP

CON

RST

 

AESP

IARB

 

SST

 

 

 

 

 

 

 

 

 

 

 

0

0

 

0

0

0

 

0

0

 

0

 

 

 

 

 

 

 

 

 

 

EXC

 

Extra Clock Cycle of Data Setup

 

 

7

 

 

When this bit is set, an extra clock period of data setup

 

 

is added to each SCSI data transfer. The extra data setup

 

 

time can provide additional system design margin, though

 

 

it affects the SCSI transfer rates. Clearing this bit disables

 

 

the extra clock cycle of data setup time. Setting this bit

 

 

only affects SCSI send operations.

 

 

 

ADB

 

Assert SCSI Data Bus

 

 

 

6

 

 

When this bit is set, the LSI53C875A drives the contents

 

 

of the SCSI Output Data Latch (SODL) register onto the

 

 

SCSI data bus. When the LSI53C875A is an initiator, the

 

 

SCSI I/O signal must be inactive to assert the SODL

 

 

contents onto the SCSI bus. When the LSI53C875A is a

 

 

target, the SCSI I/O signal must be active to assert the

 

 

SODL contents onto the SCSI bus. The contents of the

 

 

SCSI Output Data Latch (SODL) register can be asserted

 

 

at any time, even before the LSI53C875A is connected to

 

 

the SCSI bus. Clear this bit when executing SCSI

 

 

 

SCRIPTS. It is normally used only for diagnostic testing

 

 

or operation in low level mode.

 

 

 

 

DHP

 

Disable Halt on Parity Error or ATN (Target Only) 5

 

 

The DHP bit is only defined for target mode. When this

 

 

bit is cleared, the LSI53C875A halts the SCSI data

 

 

transfer when a parity error is detected or when the

 

 

SATN/ signal is asserted. If SATN/ or a parity error is

 

 

received in the middle of a data transfer, the LSI53C875A

SCSI Registers

4-23

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Image 115
LSI 53C875A technical manual Exc, Adb, Dhp