OPCOpCode27

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:

OPC Instruction Defined

0MOVE/MOVE64

1CHMOV/CHMOV64

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

Block Move Instruction

5-9

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LSI 53C875A technical manual OPCOpCode27, Target Mode, OPC Instruction Defined