chip can arbitrate with only one ID value in the SCID register.

Register: 0x4C

SCSI Test Zero (STEST0)

Read Only

7

 

 

 

4

 

3

2

1

 

0

 

 

SSAID

 

 

SLT

ART

SOZ

 

SOM

 

 

 

 

 

 

 

 

 

 

 

x

x

 

x

x

 

0

x

1

 

1

 

 

 

 

 

 

 

 

 

 

 

SSAID

 

SCSI Selected As ID

 

 

 

 

[7:4]

 

 

These bits contain the encoded value of the SCSI ID that

 

 

the LSI53C875A is selected during a SCSI selection

 

 

phase. These bits work in conjunction with the Response

 

 

ID Zero (RESPID0) and Response ID One (RESPID1)

 

 

registers, which contain the allowable IDs that the

 

 

 

LSI53C875A can respond to. During a SCSI selection

 

 

phase, when a valid ID is put on the bus, and the

 

 

 

LSI53C875A responds to that ID, the ID that the chip was

 

 

selected as will be written into the SSAID[3:0] bits.

SLT

 

Selection Response Logic Test

 

 

3

 

 

This bit is set when the LSI53C875A is ready to be

 

 

selected or reselected. This does not take into account

 

 

the bus settle delay of 400 ns. This bit is used for

 

 

 

functional test and fault purposes.

 

 

 

ART

 

Arbitration Priority Encoder Test

 

 

2

 

 

This bit is always set when the LSI53C875A exhibits the

 

 

highest priority ID asserted on the SCSI bus during

 

 

arbitration. It is primarily used for chip level testing, but it

 

 

may be used during low level mode operation to

 

 

 

determine if the LSI53C875A won arbitration.

 

SOZ

 

SCSI Synchronous Offset Zero

 

 

1

This bit indicates that the current synchronous SREQ/, SACK/ offset is zero. This bit is not latched and may change at any time. It is used in low level synchronous SCSI operations. When this bit is set, the LSI53C875A functioning as an initiator, is waiting for the target to request data transfers. If the LSI53C875A is a target, then the initiator has sent the offset number of acknowledges.

SCSI Registers

4-87

Page 179
Image 179
LSI 53C875A technical manual Register 0x4C, Ssaid, Slt, Art, Soz