Intel 8XC196NP manual Table C-14. PxREG Addresses and Reset Values, PxREG Address Table C-14

		REGISTERS
		Px_REG
Px_REG	Address:	Table C-14
x = 1–4	Reset State:

For an input, set the corresponding port x data ouput (Px_REG) register bit.

For an output, write the data to be driven out by each pin to the corresponding bit of Px_REG. When a pin is configured as standard I/O (Px_MODE.y = 0), the result of a CPU write to Px_REG is immediately visible on the pin. When a pin is configured as a special-function signal (Px_MODE.y = 1), the associated on-chip peripheral or off-chip component controls the pin. The CPU can still write to Px_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 Px_MODE.y), initialize or overwrite the pin value, then configure the pin as a special-function signal (set Px_MODE.y). In this way, initialization, fault recovery, exception handling, etc., can be done without changing the operation 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				Function
	Mnemonic
7:0	PIN7:0		Port x Pin y Output
			To use Px.y for output, write the desired output data to this bit. To use
			Px.y for input, set this bit.

Table C-14. Px_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

C-33