LSI 53C875A Computer Hardware User Manual


 
5-24 SCSI SCRIPTS Instruction Set
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. Ta ble 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
Operator
OpCode 111
Read-Modify-Write
OpCode 110
Move to SFBR
OpCode 101
Move from SFBR
000 Move data into register.
Syntax: “Move data8 to
RegA”
Move data into SCSI First
Byte Received (SFBR)
register. Syntax: “Move
data8 to SFBR”
Move data into register.
Syntax: “Move data8 to
RegA”
001
1
Shift register one bit to the
leftandplacetheresultin
the same register. Syntax:
“Move RegA SHL RegA”
Shift register one bit to the
left and place the result in
the SCSI First Byte
Received (SFBR) register.
Syntax: “Move RegA SHL
SFBR”
Shift the SFBR register one
bit to the left and place the
result in the register. Syntax:
“Move SFBR SHL RegA”
010 ORdatawithregisterand
place the result in the same
register. Syntax: “Move
RegA | data8 to RegA”
OR data with register and
place the result in the SCSI
First Byte Received (SFBR)
register. Syntax: “Move
RegA | data8 to SFBR”
OR data with SFBR and
place the result in the
register. Syntax: “Move
SFBR | data8 to RegA”
011 XOR data with register and
place the result in the same
register. Syntax: “Move
RegA XOR data8 to RegA”
XOR data with register and
place the result in the SCSI
First Byte Received (SFBR)
register. Syntax: “Move
RegA XOR data8 to SFBR”
XOR data with SFBR and
place the result in the
register. Syntax: “Move
SFBR XOR data8 to RegA”