LSI 53C875A User Manual
SCSI Functional Description
2-45
Figure 2.7
Block Move and Chained Block Move Instructions
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
(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
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
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
0x02
0x01
0x00
0x0B
0x0A
0x09
0x08
0x0F
0x0E
0x0D
0x0C
0x13
0x12
0x11
0x10
0x09
0x0B
0x0A
0x0D
0x0C
0x07
0x06
0x05
0x04
0x04
0x03
0x06
0x05
0x07
Host Memory
SCSI Bus
32 Bits
16 Bits
0x03