PIC16LC554 datasheet(23/96 Pages) MICROCHIP

23 / 96 page

Preliminary

DS40143B-page 23

PIC16C55X(A)

5.0

I/O PORTS

The PIC16C55X(A) have two ports, PORTA and PORTB.

5.1

PORTA and TRISA Registers

PORTA is a 5-bit wide latch. RA4 is a Schmitt Trigger input

and an open drain output. Port RA4 is multiplexed with the

T0CKI clock input. All other RA port pins have Schmitt

Trigger input levels and full CMOS output drivers. All pins

have data direction bits (TRIS registers) which can conﬁg-

ure these pins as input or output.

A '1' in the TRISA register puts the corresponding output

driver in a hi- impedance mode. A '0' in the TRISA register

puts the contents of the output latch on the selected pin(s).

Reading the PORTA register reads the status of the pins,

whereas writing to it will write to the port latch. All write

operations are read-modify-write operations. So a write

to a port implies that the port pins are ﬁrst read, then this

value is modiﬁed and written to the port data latch.

FIGURE 5-1:

BLOCK DIAGRAM OF

PORT PINS RA<3:0>

Note:

On reset, the TRISA register is set to all inputs.

Data

bus

PortA

TRISA

Data Latch

TRIS Latch

RD TRISA

RD PORTA

Schmitt

input

buffer

VSS

VDD

I/O pin

Trigger

FIGURE 5-2:

BLOCK DIAGRAM OF RA4 PIN

Data

bus

PORTA

TRISA

RD PORTA

Data Latch

TRISA Latch

RD TRISA

Schmitt

Trigger

input

buffer

VSS

I/O pin(1)

TMR0 clock input

Note 1: I/O pin has protection diodes to VSS only.

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