LSI 53C810A First Dword, IT10 Instruction Type Block Move 3130 Indirect Addressing

6.3.1 First Dword

IT[1:0]	Instruction Type - Block Move		[31:30]
IA	Indirect Addressing		29
	When this bit is cleared, user data is moved to or from
	the 32-bit data start address for the Block Move
	instruction. The value is loaded into the chip’s address
	register and incremented as data is transferred. The
	address of data to be moved is in the second Dword of
	this instruction.
	When set, the 32-bit user data start address for the Block
	Move is the address of a pointer to the actual data buffer
	address. The value at the 32-bit start address is loaded
	into the chip’s DMA Next Address (DNAD) register using
	a third Dword fetch (4-byte transfer across the host
	computer bus).
	Direct Addressing
	The byte count and absolute address are:
	Command	Byte Count

Address of Data

Indirect Addressing

Use the fetched byte count, but fetch the data address from the address in the instruction.

Command Byte Count

Address of Pointer to Data

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 SCRIPTS file when the program is assembled. 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.

6-6 Instruction Set of the I/O Processor