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5-12 SCSI SCRIPTS Instruction Set
TC[23:0] Transfer Counter [23:0]
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 DMA Byte Counter (DBC)
register. When the LSI53C875A transfers data to/from
memory, the DBC register is decremented by the number
of bytes transferred. In addition, the DMA Next Address
(DNAD) register is incremented by the number of bytes
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 Data Structure Address (DSA)
register.
Table 5.2 SCSI Information Transfer Phase
MSG C_D I_O SCSI Phase
000Data-Out
001Data-In
0 1 0 Command
011Status
1 0 0 Reserved
1 0 1 Reserved
1 1 0 Message-Out
1 1 1 Message-In