LSI 53C875A - Manual (Page 209)

Block Move Instruction 5-9
OPC OpCode 27
This 1-bit OpCode field defines the type of Block Move
(MOVE) Instruction to be preformed in Target and Initiator
mode.
Target Mode
In Target mode, the OpCode bit defines the following
operations:
These instructions perform the following steps:
1. The LSI53C875A verifies that it is connected to the SCSI
bus as a Target before executing this instruction.
2. The LSI53C875A asserts the SCSI phase signals (SMSG/,
SC_D/, and SI_O/) as defined by the Phase Field bits in the
instruction.
3. If the instruction is for the command phase, the
LSI53C875A receives the first command byte and decodes
its SCSI Group Code.
– If the SCSI Group Code is either Group 0, Group 1,
Group 2, or Group 5, and if the Vendor Unique
Enhancement 1 (VUE1) bit (SCNTL2 bit 1) is clear, then
the LSI53C875A overwrites the
DMA Byte Counter
(DBC) register with the length of the Command
Descriptor Block: 6, 10, or 12 bytes.
– If the Vendor Unique Enhancement 1 (VUE1) bit
(SCNTL2 bit 1) is set, the LSI53C875A receives the
number of bytes in the byte count regardless of the
group code.
– If the Vendor Unique Enhancement 1 bit is clear and
group code is vendor unique, the LSI53C875A receives
the number of bytes in the count.
– If any other Group Code is received, the DMA Byte
Counter (DBC) register is not modified and the
LSI53C875A requests the number of bytes specified in
the
DMA Byte Counter (DBC) register. If the DBC
OPC Instruction Defined
0 MOVE/MOVE64
1 CHMOV/CHMOV64