LSI LSI53C1000, Technical Manual

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5-10 SCSI SCRIPTS Instruction Set
Target Mode
The LSI53C1000 verifies that it is connected to the SCSI
bus as a target before executing this instruction.
The LSI53C1000 asserts the SCSI phase signals
(SMSG/, SC_D/, and SI_O/) as defined by the Phase
Field bits in the instruction.
If the instruction is for the command phase, the
LSI53C1000 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, then the LSI53C1000
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 0 (VUE0) bit
(
SCSI Control Two (SCNTL2) , bit 1) is cleared and the
SCSI group code is a vendor unique code, the
LSI53C1000 overwrites the
DMA Byte Counter (DBC)
register with the length of the Command Descriptor
Block: 6, 10, or 12 bytes. If the VUE0 bit is set, the
LSI53C1000 receives the number of bytes in the byte
count regardless of the group code.
•
If any other Group Code is received, the DMA Byte
Counter (DBC) register is not modified and the
LSI53C1000 requests the number of bytes specified
in the
DMA Byte Counter (DBC) register. If the DBC
register contains 0x000000, an illegal instruction
interrupt is generated.
The LSI53C1000 transfers the number of bytes specified
in the
DMA Byte Counter (DBC) register starting at the
address specified in the DMA Next Address (DNAD)
register. If the Opcode bit is set and a data transfer ends
on an odd byte boundary, the LSI53C1000 stores the last
byte in the
SCSI Wide Residue (SWIDE) register during
OPC Instruction Defined
0 MOVE/MOVE64
1 CHMOV/CHMOV64