253
5-22-5 EXCLUSIVE NOR – XNRW(37)
I1:
Input 1
IR, SR, AR, DM, HR, TC, LR, #
I2
: Input 2
IR, SR, AR, DM, HR, TC, LR, #
Ladder Symbols
Operand Data Areas
R: Result word
IR, SR, AR, DM, HR, LR
XNRW(37)
I1
I2
R
@XNRW(37)
I1
I2
R
Description When
the execution condition is OFF
, XNR
W(37) is
not executed. When the ex
-
ecution
condition is ON,
XNR
W(37) exclusively NOR’
s the contents of I1 and I2
bit-by-bit and places the result in R.
10 01100110011001
15 00
01 01010101010101
00 11001100110011
15 00
15 00
I1
I2
R
Flags ER: Indirectly
addressed
DM word is non-existent. (Content of
:
DM word is
not BCD, or the DM area boundary has been exceeded.)
EQ: ON when the result is 0.
5-23 Subroutines and Interrupt Control
5-23-1 Subroutines
Subroutines
break large control tasks into smaller ones and enable
you to reuse
a
given set of instructions. When the main program calls a subroutine, control is
transferred
to the subroutine and the subroutine instructions are executed. The
instructions within a subroutine are written in the same way as main program
code.
When all the subroutine instructions have been executed, control returns
to the main program to the point just after the point from which the subroutine
was entered (unless otherwise specified in the subroutine).
Subroutines may also be activated by interrupts or the MCRO(99) instruction.
Interrupts Like subroutine calls, interrupts cause
a break in the flow of the main program
execution
such that the flow can be resumed from that point after completion of
the
subroutine. An interrupt is
caused either by an external source, such as an
input
signal from an Interrupt Input
Unit, or a scheduled interrupt. In the case of
the scheduled interrupt, the interrupt signal is repeated at regular intervals.
Whereas
subroutine calls are controlled from within the main program, subrou
-
tines
activated by interrupts are triggered when the interrupt signal is
received.
In
the case of the scheduled interrupt, the time interval between interrupts is set
by
the user and is unrelated to the cycle timing of the PC. This
capability is useful
for periodic supervisory or executive program execution.
Subroutines and Interrupt Control Section 5-23
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