LSI 53C875A User Manual
Page 207
Block Move Instruction
5-7
Direct Addressing
The byte count and absolute address are:
Indirect Addressing
Use the fetched byte count, but fetch the data address
from the address in the instruction.
Once the data pointer address is loaded, it is executed
as when the chip operates in the direct mode. This
indirect feature allows a table of data buffer addresses to
be specified. Using the SCSI SCRIPTS assembler, the
table offset is placed in the script at compile time. Then
at the actual data transfer time, the offsets are added to
the base address of the data address table by the
external processor. The logical I/O driver builds a
structure of addresses for an I/O rather than treating each
address individually. This feature makes it possible to
locate SCSI SCRIPTS in a PROM.
Note:
Do not use indirect and table indirect addressing
simultaneously; use only one addressing method at a time.
TIA
Table Indirect
28
32-Bit Addressing
When this bit is set, the 24-bit signed value in the start
address of the move is treated as a relative displacement
from the value in the
register. Both the transfer count and the source/
destination address are fetched from this location.
Use the signed integer offset in bits [23:0] of the second
four bytes of the instruction, added to the value in the
register, to fetch first the
byte count and then the data address. The signed value
is combined with the data structure base address to
generate the physical address used to fetch values from
Command
Byte Count
Address of Data
Command
Byte Count
Address of Pointer to Data