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SCSI Registers 4-63
LSI53C875A. The DBC counter is decremented each
time data is transferred on the PCI bus. It is decremented
by an amount equal to the number of bytes that are
transferred.
The maximum number of bytes that can be transferred in
any one Block Move command is 16,777,215 bytes. The
maximum value that can be loaded into the DMA Byte
Counter (DBC) register is 0xFFFFFF. If the instruction is
a Block Move and a value of 0x000000 is loaded into the
DBC register, an illegal instruction interrupt occurs if the
LSI53C875A is not in target mode, Command phase.
The DBC register is also used to hold the least significant
24 bits of the first Dword of a SCRIPTS fetch, and to hold
the offset value during table indirect I/O SCRIPTS. For a
complete description see Chapter 5, “SCSI SCRIPTS
Instruction Set”. The power-up value of this register is
indeterminate.
See Section 5.3.1, “First Dword,” for register detail.
Register: 0x27
DMA Command (DCMD)
Read/Write
DCMD DMA Command [7:0]
This 8-bit register determines the instruction for the
LSI53C875A to execute. This register has a different
format for each instruction.
See Section 5.3.1, “First Dword,” for register detail.
7 0
DCMD
01xxxxxx