Scsi Information Transfer Phase - LSI LSI53C875A Technical Manual

5-12
Table 5.2
MSG C_D
0
0
0
0
1
1
1
1
TC[23:0] Transfer Counter
This 24-bit field specifies the number of data bytes to be
moved between the LSI53C875A and system memory.
The field is stored in the
register. When the LSI53C875A transfers data to/from
memory, the DBC register is decremented by the number
of bytes transferred. In addition, the
(DNAD)
transferred. This process is repeated until the DBC
register is decremented to zero. At this time, the
LSI53C875A fetches the next instruction.
If bit 28 is set, indicating table indirect addressing, this
field is not used. The byte count is instead fetched from
a table pointed to by the
register.
SCSI SCRIPTS Instruction Set

SCSI Information Transfer Phase

I_O SCSI Phase
0 0 Data-Out
0 1 Data-In
1 0 Command
1 1 Status
0 0 Reserved
0 1 Reserved
1 0 Message-Out
1 1 Message-In
DMA Byte Counter (DBC)
register is incremented by the number of bytes
Data Structure Address (DSA)
[23:0]
DMA Next Address