DS80C320-ECD DALLAS [Dallas Semiconductor], DS80C320-ECD Datasheet - Page 119

• Manufacturer Part Number: DS80C320-ECD
• Description: High-Speed Microcontroller User Guide
• Manufacturer: DALLAS [Dallas Semiconductor]

READ-MODIFY-WRITE INSTRUCTIONS
The normal read instructions will read the pin state without regard to the output data latch. The only
exception is the read-modify–write category of instructions. They are listed as follows.
INSTRUCTION DESCRIPTION
ANL
ORL
XRL
JBC
CPL
INC
DEC
DJNZ
MOV PX.n, C
CLR PX.n
SETB PX.n
The read-modify-write instructions read the state of the latch, then write back the result to the latch. Thus
the operation takes place using the value that was originally written to the SFR, without regard to the pin
state. The last three instructions listed above are read-modify-write because they read the entire port
latch, then write back the changed value. In this case, only one bit will be changed as specified by the
instruction.
I/O PORT TIMING
Figure 10-1 shows when port pins change in relationship to instruction timing. The example shown uses
a MOV command to change P1.0 from a logic 1 to a logic 0. This diagram is presented to aid the
designer in determining the timing relationship for very critical designs. Most designers will not need to
consider this much detail. Dummy NOP instructions are shown to illustrate subsequent instructions.
Logical AND
Logical OR
Logical Exclusive OR (XOR)
Branch if bit set then clear bit
Complement bit
Increment
Decrement
Decrement and branch if not zero
Move the carry bit to bit n of port X
Clear bit n of port X
Set bit n of port X
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High-Speed Microcontroller User’s Guide