
Instruction Set of the I/O Processor
Transfer Control Instructions
SYM53C810A Data Manual
6-19
2. If the comparisons are false, then the
SYM53C810A fetches the next instruction
from the address pointed to by the DSP
register and the instruction pointer will not be
modified.
Interrupt Instructions
Interrupt
a) T he SYM53C810A 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 the
SYM53C810A generates an interrupt by
asserting the IRQ/ signal.
b) T he 32-bit address field stored in the
DSPS register (not DNAD as in 53C700)
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.
c) T he SYM53C810A halts and the DSP
register must be written to start any further
operation.
Interrupt on-the-Fly
a) T he SYM53C810A 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 is set (bit 20), the
SYM53C810A will assert the Interrupt on
the Fly bit (ISTAT bit 2).
Bits 26-24 SCSI Phase
T his 3-bit field corresponds to the three SCSI
bus phase signals which 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. T he following table describes the
possible combinations and their correspond-
ing SCSI phase. T hese bits are only valid when
the SYM53C810A is operating in initiator
mode; when the SYM53C810A is operating in
the target mode, these bits should be cleared.
Bit 23 Relative Addressing Mode
When this bit is set, the 24-bit signed value in
the DSPS register is used as a relative offset
from the current DSP address (which is point-
ing to the next instruction, not the one cur-
rently executing). Relative mode does not
apply to Return and Interrupt SCRIPT S.
Jump/Call an Absolute Address
Start execution at the new absolute address.
Jump/Call a Relative Address
Start execution at the current address plus (or
minus) the relative offset.
T he SCRIPT S program counter is a 32-bit
value pointing to the SCRIPT S instruction
currently being executed by the
SYM53C810A. T he next address is formed by
adding the 32-bit program counter to the 24-
bit signed value of the last 24 bits of the Jump
MSG
C/D
I/O
SCSI Phase
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Data out
Data in
Command
Status
Reserved out
Reserved in
Message out
Message in
Command
Condition Codes
Absolute Alternate Address
Command
Don’t Care
Condition Codes
Alternate Jump Offset