Dma byte counter (dbc), Byte counter (dbc) – Avago Technologies LSI53C895A User Manual
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Registers
Registers: 0x24–0x26
DMA Byte Counter (DBC)
Read/Write
DBC
DMA Byte Counter
[23:0]
This 24-bit register determines the number of bytes
transferred in a Block Move instruction. While sending
data to the SCSI bus, the counter is decremented as data
is moved into the DMA FIFO from memory. While
receiving data from the SCSI bus, the counter is
decremented as data is written to memory from the
LSI53C895A. 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
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
LSI53C895A 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
The power-up value of this register is
indeterminate.
23
0
DBC
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x