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Example:
INSTRUCTION SET
Decrement contents
of
external data memory location
63.
MOV
RO,#3FH
;MOVE '3F' HEX TO
REG
0
MOVX
A,@RO
;MOVE CONTENTS
OF
LOCATION
63
DEC A
MOVX
@RO,A
;TO ACC
;DECREMENT ACC
;MOVE CONTENTS
OF
ACC TO
;LOCATION
63
IN EXPANDED
;MEMORY
DEC
Rr
Decrement
Register
1110011rrri
(Not in 8021, 8022)
The contents
of
working register 'r' are decremented
by one.
(Rr)--
(Rr)-1 r=0-7
Example: DECR1: DEC
R1
;DECREMENT CONTENTS
OF
REG
1
DIS I Disable
External
Interrupt (Not in 8021)
10001101011
External interrupts are disabled. A low signal on
the interrupt input pin has no effect.
DIS TCNTI Disable Timer/Counter Interrupt (Not in 8021)
10011101011
Timer/counter interrupts are disabled. Any pending
timer interrupt request is
cleared. The interrupt
sequence
is
not initiated by
an
overflow, but the
timer
flag
is
set and time accumulation continues.
DJNZ
Rrl
address Decrement Register and Test
11
1 1 0
11
r r r 1 1
a7
a6
a5 a4
1
a3 a2
a1
ao
1
This
is
a 2-cycle instruction. Register 'r'
is
decremented and tested
for
zero. If the register
contains
all zeros, program control falls through
to the next instruction.
If the register contents
are not zero,
control jumps to the specified 'address'.
The address in this case must
evaluate to 8-bits, that
is, the jump must
be
to a location within the current
256-location page.
(Rr)--
(Rr)-1 r=0-7
If
Rr
not 0
(PCO-7)-- addr
Mnemonics copyright Intel Corporation
1976.
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