Figure 2.7 Block Move and Chained Block Move Instructions

Host Memory

0x03

0x02

0x01

0x00

 

 

 

 

0x07

0x06

0x05

0x04

 

 

 

 

0x0B

0x0A

0x09

0x08

 

 

 

 

0x0F

0x0E

0x0D

0x0C

 

 

 

 

0x13

0x12

0x11

0x10

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

32 Bits

SCSI Bus

0x04

0x03

 

 

0x06

0x05

 

 

 

 

 

 

0x09

0x07

 

 

0x0B

0x0A

 

 

0x0D

0x0C

 

 

 

 

16 Bits

2.2.17.1 Wide SCSI Send Bit

The WSS bit is set whenever the SCSI controller is sending data (Data-Out for initiator or Data-In for target) and the controller detects a partial transfer at the end of a chained Block Move SCRIPTS instruction (this flag is not set if a normal Block Move instruction is used). Under this condition, the SCSI controller does not send the low-order byte of the last partial memory transfer across the SCSI bus. Instead, the low-order byte is temporarily stored in the lower byte of the SCSI Output Data Latch (SODL) register and the WSS flag is set. The hardware uses the WSS flag to determine what behavior must occur at the start of the next data send transfer. When the WSS flag is set at the start of the next transfer, the first byte (the high-order byte) of the next data send transfer is “married” with the stored low-order byte in the SODL register; and the

SCSI Functional Description

2-45

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LSI 53C875A technical manual Block Move and Chained Block Move Instructions, Wide Scsi Send Bit