ACK

Set/Clear SACK/

6

ATN

Set/Clear SATN/

3

 

These two bits are used in conjunction with a Set or Clear

 

instruction to assert or deassert the corresponding SCSI

 

control signal. Bit 6 controls the SCSI SACK/ signal. Bit 3

 

controls the SCSI SATN/ signal.

 

 

Setting either of these bits sets or resets the

 

 

corresponding bit in the SCSI Output Control Latch

 

 

(SOCL) register, depending on the instruction used. The

 

Set instruction is used to assert SACK/ and/or SATN/ on

 

the SCSI bus. The Clear instruction is used to deassert

 

SACK/ and/or SATN/ on the SCSI bus.

 

 

Since SACK/ and SATN/ are Initiator signals, they are not

 

asserted on the SCSI bus unless the LSI53C810A is

 

operating as an Initiator or the SCSI Loopback Enable bit

 

is set in the SCSI Test Two (STEST2) register.

 

 

The Set/Clear SCSI ACK/ATN instruction is used after

 

message phase Block Move operations to give the

 

 

Initiator the opportunity to assert attention before

 

 

acknowledging the last message byte. For example, if the

 

initiator wishes to reject a message, it issues an Assert

 

SCSI ATN instruction before a Clear SCSI ACK

 

 

instruction.

 

R

Reserved

[2:0]

6.4.2 Second Dword

SAStart Address[31:0]

This 32-bit field contains the memory address to fetch the next instruction if the selection or reselection fails.

If relative or table relative addressing is used, this value is a 24-bit signed offset relative to the current DMA SCRIPTS Pointer (DSP) register value.

6-22

Instruction Set of the I/O Processor

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LSI 53C810A technical manual Set/Clear Sack, Set/Clear Satn, SAStart Address310