5.5.4 Move To/From SFBR Cycles

All operations are read-modify-writes. However, two registers are involved, one of which is always the SFBR. Table 5.3 shows the possible read-modify-write operations. The possible functions of this instruction are:

Write one byte (value contained within the SCRIPTS instruction) into any chip register.

Move to/from the SFBR from/to any other register.

Alter the value of a register with AND, OR, ADD, XOR, SHIFT LEFT, or SHIFT RIGHT operators.

After moving values to the SFBR, the compare and jump, call, or similar instructions are used to check the value.

A Move-to-SFBR followed by a Move-from-SFBR is used to perform a register-to-register move.

Table 5.3

Read/Write Instructions

 

 

 

 

 

 

OpCode 111

OpCode 110

OpCode 101

Operator

Read-Modify-Write

Move to SFBR

Move from SFBR

 

 

 

 

000

Move data into register.

Move data into SCSI First

Move data into register.

 

Syntax: “Move data8 to

Byte Received (SFBR)

Syntax: “Move data8 to

 

RegA”

register. Syntax: “Move

RegA”

 

 

data8 to SFBR”

 

 

 

 

 

0011

Shift register one bit to the

Shift register one bit to the

Shift the SFBR register one

 

left and place the result in

left and place the result in

bit to the left and place the

 

the same register. Syntax:

the SCSI First Byte

result in the register. Syntax:

 

“Move RegA SHL RegA”

Received (SFBR) register.

“Move SFBR SHL RegA”

 

 

Syntax: “Move RegA SHL

 

 

 

SFBR”

 

 

 

 

 

010

OR data with register and

OR data with register and

OR data with SFBR and

 

place the result in the same

place the result in the SCSI

place the result in the

 

register. Syntax: “Move

First Byte Received (SFBR)

register. Syntax: “Move

 

RegA data8 to RegA”

register. Syntax: “Move

SFBR data8 to RegA”

 

 

RegA data8 to SFBR”

 

 

 

 

 

011

XOR data with register and

XOR data with register and

XOR data with SFBR and

 

place the result in the same

place the result in the SCSI

place the result in the

 

register. Syntax: “Move

First Byte Received (SFBR)

register. Syntax: “Move

 

RegA XOR data8 to RegA”

register. Syntax: “Move

SFBR XOR data8 to RegA”

 

 

RegA XOR data8 to SFBR”

 

 

 

 

 

5-24

SCSI SCRIPTS Instruction Set

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LSI 53C875A technical manual Move To/From Sfbr Cycles, Read/Write Instructions