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CHAPTER 12 PORTS
12.1 PORT 0A (P0A
0
, P0A
1
, P0A
2
, P0A
3
)
Port 0A is a 4-bit input/output port with an output latch. It is mapped into address 70H of BANK0 in data memory.
The output format is CMOS push-pull output.
Input or output can be specified in each bit. Input/output is specified by P0ABIO0 to P0ABIO3 (address 35H) in
the register file.
When P0ABIOn is 0 (n=0 to 3), each pin of port 0A is used as input port. If a read instruction is executed for the
port register, pin statuses are read.
When P0ABIOn is 1 (n=0 to 3), each pin of port 0A is used as output port and the contents written in the output
latch are output to pins. If a read instruction is executed when pins are output ports, the contents of the output latch,
rather than pin statuses, are fetched.
At reset, P0ABIOn is set to 0 and all P0A pins become input ports. The contents of the port output latch are 0.
Table 12-1. Writing into and Reading from the Port Register (0.70H)
BANK0 70H
Write
Read
0
Input
P0A pin status
1
Output
P0A latch contents
P0ABIOn
RF: 35H
Pin Input/Output
Possible
Write to the P0A
latch
105
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