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5-26 SCSI SCRIPTS Instruction Set
5.6.1 First Dword
IT[1:0] Instruction Type - Transfer Control
Instruction [31:30]
The IT bit configuration (10) defines the Transfer Control
Instruction Type.
OPC[2:0] OpCode [29:27]
This 3-bit field specifies the type of Transfer Control
Instruction to execute. All Transfer Control Instructions
can be conditional. They can be dependent on a
true/false comparison of the ALU Carry bit or a
comparison of the SCSI information transfer phase with
the Phase field, and/or a comparison of the First Byte
Received with the Data Compare field. Each instruction
can operate in Initiator or Target mode. Transfer Control
Instructions are shown in Table 5.4 .
Jump Instruction
The LSI53C875A can do a true/false comparison of the
ALU carry bit, or compare the phase and/or data as
defined by the Phase Compare, Data Compare and
True/False bit fields.
If the comparisons are true, then it loads the DMA
SCRIPTS Pointer (DSP) register with the contents of the
31 30 29 27 26 24 23 22 21 20 19 18 17 16 15 8 7 0
DMA Command (DCMD)
Register
DMA Byte Counter (DBC) Register
IT[1:0] OPC[2:0] SCSIP[2:0] RA
R CT IF JMP CD CP WVP
DCM-Data Compare
Mask
DCV-Data Compare
Value
10xxxx x xx
0 x x x x x x xxxxxxxxxxxxxxxx
Table 5.4 Transfer Control Instructions
OPC2 OPC1 OPC0 Instruction Defined
000Jump
001Call
010Return
0 1 1 Interrupt
1 X X Reserved