5.6.1 First Dword

31 30 29

27

26

24

23 22

21

20

19

18

 

17

 

16

15

8

 

7

0

DMA Command (DCMD)

 

 

 

 

 

 

 

 

 

DMA Byte Counter (DBC) Register

 

 

 

 

 

Register

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

IT[1:0]

OPC[2:0]

SCSIP[2:0]

RA

R

CT

IF

JMP

CD

CP

WVP

 

DCM-Data Compare

 

 

DCV-Data Compare

 

Mask

 

 

 

Value

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1 0

x x x

x x x

x

0

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 - 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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 5.4

Transfer Control Instructions

 

 

 

 

 

 

 

 

 

 

 

OPC2

 

 

OPC1

OPC0

Instruction Defined

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0

 

 

 

0

 

0

Jump

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0

 

 

 

0

 

1

Call

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0

 

 

 

1

 

0

Return

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0

 

 

 

1

 

1

Interrupt

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1

 

 

 

X

 

X

Reserved

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

5-26

SCSI SCRIPTS Instruction Set

Page 226
Image 226
LSI 53C875A technical manual IT10 Instruction Type Transfer Control 3130, Transfer Control Instructions, Jump Instruction