LSI LSI53C895A, Technical Manual

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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 LSI53C895A and system memory.
The field is stored in the
DMA Byte Counter (DBC)
register. When the LSI53C895A 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
LSI53C895A 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.
5.3.2 Second Dword
Start Address [31:0]
This 32-bit field specifies the starting address of the data
to move to/from memory. This field is copied to the
DMA
Next Address (DNAD) register. When the LSI53C895A
transfers data to or from memory, the DNAD register is
incremented by the number of bytes transferred.
When bit 29 is set, indicating indirect addressing, this
address is a pointer to an address in memory that points
to the data location. When bit 28 is set, indicating table
indirect addressing, the value in this field is an offset into
a table pointed to by the
Data Structure Address (DSA) .
The table entry contains byte count and address
information.
31 24 23 16 15 8 7 0
DMA SCRIPTS Pointer Save (DSPS) Register
x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x