
Transfer Control Instructions
5-29
When a Return instruction is executed, the value stored
in the
Temporary (TEMP)
register is returned to the
DMA
SCRIPTS Pointer (DSP)
register. The SYM53C1010-33
does not check to see whether the Call instruction has
already been executed. It does not generate an interrupt
if a Return instruction is executed without previously
executing a Call instruction.
If the comparisons are false, the SYM53C1010-33
fetches the next instruction from the address pointed to
by the
DMA SCRIPTS Pointer (DSP)
register and the
instruction pointer is not modified.
Interrupt Instruction
The SYM53C1010-33 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, the
SYM53C1010-33 generates an interrupt by asserting the
IRQ/ signal.
The 32-bit address field stored in the
DMA SCRIPTS
Pointer Save (DSPS)
register can contain a unique
interrupt service vector. When servicing the interrupt, this
unique status code allows the ISR to quickly identify the
point at which the interrupt occurred.
The SYM53C1010-33 halts and the
DMA SCRIPTS
Pointer (DSP)
register must be written to before starting
any further operation.
Interrupt-on-the-Fly Instruction
The SYM53C1010-33 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, and the
Interrupt-on-the-Fly bit
Interrupt Status Zero (ISTAT0)
, bit
2) is set, the SYM53C1010-33 asserts the Interrupt-on-
the-Fly bit.
SCSIP[2:0]
SCSI Phase
This 3-bit field corresponds to the three SCSI bus phase
signals that are compared with the phase lines latched
when SREQ/ is asserted. Comparisons can be performed
to determine the SCSI phase actually being driven on the
SCSI bus. The following table describes the possible
[26:24]