Intel 80C196NU User Manual
C-33
REGISTERS
Px_REG
P
x
_REG
x
= 1–4
Address:
Reset State:
Table C-14
For an input, set the corresponding port x data ouput (P
x
_REG) register bit.
For an output, write the data to be driven out by each pin to the corresponding bit of P
x
_REG. When a
pin is configured as standard I/O (P
x
_MODE.
y
= 0), the result of a CPU write to P
x
_REG is
immediately visible on the pin. When a pin is configured as a special-function signal (P
x
_MODE.
y
= 1),
the associated on-chip peripheral or off-chip component controls the pin. The CPU can still write to
P
P
x
_REG, but the pin is unaffected until it is switched back to its standard I/O function.
This feature allows software to configure a pin as standard I/O (clear P
x
_MODE.
y
), initialize or
overwrite the pin value, then configure the pin as a special-function signal (set P
x
_MODE.
y
). In this
way, initialization, fault recovery, exception handling, etc., can be done without changing the operation
of the associated peripheral.
of the associated peripheral.
7
0
x
= 1–3
PIN7
PIN6
PIN5
PIN4
PIN3
PIN2
PIN1
PIN0
7
0
x
= 4
—
—
—
—
PIN3
PIN2
PIN1
PIN0
Bit Number
Bit
Mnemonic
Function
7:0
PIN7:0
Port
x
Pin
y
Output
To use P
x
.
y
for output, write the desired output data to this bit. To use
P
x
.
y
for input, set this bit.
Table C-14. P
x_REG Addresses and Reset Values
Register
Address
Reset Value
P1_REG
1FD4H
FFH
P2_REG
1FD5H
FFH
P3_REG
1FDCH
FFH
P4_REG
1FDDH
FFH