PIC16LC505-20SLASHP datasheet(19/80 Pages) MICROCHIP

19 / 80 page

Preliminary

DS40192A-page 19

PIC16C505

5.0

I/O PORT

As with any other register, the I/O register can be

written and read under program control. However,

read instructions (e.g., MOVF PORTB,W) always read

the I/O pins independent of the pin’s input/output

modes. On RESET, all I/O ports are deﬁned as input

(inputs are at hi-impedance) since the I/O control

registers are all set.

5.1

PORTB

PORTB is an 8-bit I/O register. Only the low order 6

bits

are

used

(RB5:RB0).

Bits

and

are

unimplemented and read as '0's. Please note that RB3

is an input only pin. The conﬁguration word can set

several I/O’s to alternate functions. When acting as

alternate functions the pins will read as ‘0’ during port

read. Pins RB0, RB1, RB3 and RB4 can be conﬁgured

with weak pull-ups and also with wake-up on change.

The wake-up on change and weak pull-up functions

are not pin selectable. If pin 4 is conﬁgured as MCLR,

weak pull-up is always off and wake-up on change for

this pin is not enabled.

5.2

PORTC

PORTC is an 8-bit I/O register. Only the low order 6

bits are used (RC5:RC0). Bits 7 and 6 are unimple-

mented and read as ‘0’s.

5.3

TRIS Registers

The output driver control register is loaded with the

contents of the W register by executing the TRIS f

instruction. A '1' from a TRIS register bit puts the

corresponding output driver in a hi-impedance mode.

A '0' puts the contents of the output data latch on the

selected

pins,

enabling

the

output

buffer. The

exceptions are RB3 which is input only and RC5 which

may be controlled by the option register, see Figure 4-

The TRIS registers are “write-only” and are set (output

drivers disabled) upon RESET.

Note:

A read of the ports reads the pins, not the

output data latches. That is, if an output

driver on a pin is enabled and driven high,

but the external system is holding it low, a

read of the port will indicate that the pin is

low.

5.4

I/O Interfacing

The equivalent circuit for an I/O port pin is shown in

Figure 5-1. All port pins, except RB3 which is input

only, may be used for both input and output

operations. For input operations these ports are non-

latching. Any input must be present until read by an

input instruction (e.g., MOVF PORTB,W). The outputs

are latched and remain unchanged until the output

latch is rewritten. To use a port pin as output, the

corresponding direction control bit in TRIS must be

cleared (= 0). For use as an input, the corresponding

TRIS bit must be set. Any I/O pin (except RB3) can be

programmed individually as input or output.

FIGURE 5-1:

EQUIVALENT CIRCUIT

FOR A SINGLE I/O PIN

Note 1: I/O pins have protection diodes to VDD and VSS.

Data

Bus

Port

TRIS ‘f’

Data

TRIS

RD Port

VSS

VDD

I/O

pin(1)

Reg

Latch

Reset

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