5.3 Block Move Instruction

Performing a Block Move instruction, bit 5, Source I/O - Memory Enable (SIOM) and bit 4, Destination I/O - Memory Enable (DIOM) in the DMA Mode (DMODE) register determines whether the source/destination address resides in memory or I/O space. When data is being moved onto the SCSI bus, SIOM controls whether that data comes from I/O or memory space. When data is being moved off of the SCSI bus, DIOM controls whether that data goes to I/O or memory space.

5.3.1 First Dword

31

30

29

28

27

26

24

23

0

DMA Command (DCMD) Register

 

DMA Byte Counter (DBC) Register

 

 

 

 

 

 

 

 

IT[1:0]

IA

TIA

OPC

SCSIP[2:0]

 

 

Transfer Counter [23:0]

 

 

 

 

 

 

 

0 0

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

 

 

 

 

 

 

 

 

 

 

 

IT[1:0]

Instruction Type - Block Move

[31:30]

 

The IT bit configuration (00) defines a Block Move

 

Instruction Type.

 

IA

Indirect Addressing

29

This bit determines if addressing is direct or indirect.

If IA bit is (0), use destination field as an address (direct addressing). If IA bit is (1), use destination field as a pointer to an address (indirect addressing).

When this bit is zero, 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 the data to move is in the second Dword of this instruction.

When this bit is one, 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 longword fetch (4-byte transfer across the host computer bus).

5-6

SCSI SCRIPTS Instruction Set

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LSI 53C875A technical manual Block Move Instruction, First Dword