a byte stored in system memory, the byte must first be moved to an intermediate LSI53C875A register (such as a SCRATCH register), and then to the SFBR.

This register also contains the state of the lower eight bits of the SCSI data bus during the Selection phase if the COM bit in the DMA Control (DCNTL) register is clear.

If the COM bit is cleared, do not access this register using SCRIPTS operations, as nondeterminate operations may occur. This includes SCRIPTS Read/Write operations and conditional transfer control instructions that initialize the SFBR register.

Register: 0x09

SCSI Output Control Latch (SOCL)

Read/Write

7

6

5

4

3

2

1

0

REQ

ACK

 

BSY

SEL

ATN

MSG

C_D

I/O

 

 

 

 

 

 

 

 

 

0

0

 

0

0

0

0

0

0

 

 

 

 

 

 

 

 

 

REQ

 

Assert SCSI REQ/ Signal

 

 

7

ACK

 

Assert SCSI ACK/ Signal

 

 

6

BSY

 

Assert SCSI BSY/ Signal

 

 

5

SEL

 

Assert SCSI SEL/ Signal

 

 

4

ATN

 

Assert SCSI ATN/ Signal

 

 

3

MSG

 

Assert SCSI MSG/ Signal

 

 

2

C_D

 

Assert SCSI C_D/ Signal

 

 

1

I/O

 

Assert SCSI I_O/ Signal

 

 

0

This register is used primarily for diagnostic testing or programmed I/O operation. It is controlled by the SCRIPTS processor when executing SCSI SCRIPTS. SOCL is used only when transferring data using programmed I/O. Some bits are set (1) or cleared (0) when executing SCSI SCRIPTS. Do not write to the register once the LSI53C875A starts executing normal SCSI SCRIPTS.

SCSI Registers

4-37

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LSI 53C875A technical manual Req, Ack, Bsy, Sel, Atn, Msg