Avago Technologies LSI53C1010 - Manual (Page 101)

Instruction Descriptions 3-61
Description The SCSI RETURN instruction is a conditional return from a subroutine
to the effective address, stored in the chip's TEMP register, if the SCSI
phase, data, or attention condition compares true with the condition
specified in the instruction.
When the optional data field is used, it is compared to the SFBR. This
contains the most recent byte of any kind of data that has been moved
into the SFBR register. The SCSI SCRIPTS program determines which
routine to execute next based on actual data values received. Using a
series of these comparisons, the algorithm processes complex
sequences with no intervention required by the external processor.
When the optional MASK keyword and its associated value are specified
the SCRIPTS processor allows selective comparisons of bits within the
data byte. During the comparison, any bits that are set in the mask byte
will cause the corresponding bit in the data byte to be ignored for the
comparison.
Notes If a RETURN instruction is executed without any previous CALL
instruction, then there is no proper return address in the chip's TEMP
register. This may cause the chip to generate an illegal opcode after the
return.
Legal Forms RETURN
RETURN, IF ATN
RETURN, IF Phase
RETURN, IF CARRY
RETURN, IF data
RETURN, IF data AND MASK data
RETURN, IF ATN AND data
RETURN, IF ATN AND data AND MASK data
RETURN, IF Phase AND data
RETURN, IF Phase AND data AND MASK data
Mask An 8-bit field that masks the value in SFBR before the
comparison with the data field in the instruction takes place. As
a result of this operation, any bits that are set cause the
corresponding bit in the data byte to be ignored. If this field is
not specified, a mask of 0x00 is used.
Data An 8-bit field that is compared with the incoming data after the
mask operation with the mask byte takes place. Comparison
indicates either an equal or not equal condition. If the Data field
is not specified, the compare data bit is cleared and 0x00 is
coded for both the mask and data bytes.