10F222 datasheet(23/86 Pages) MICROCHIP

23 / 86 page

DS41270E-page 21

PIC10F220/222

5.0

I/O PORT

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

written and read under program control. However, read

instructions (e.g., MOVF GPIO, 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

high-impedance) since the I/O control registers are all

set.

5.1

GPIO

GPIO is an 8-bit I/O register. Only the low-order 4 bits

are used (GP<3:0>). Bits 7 through 4 are unimple-

mented and read as ‘0’s. Please note that GP3 is an

input only pin. Pins GP0, GP1 and GP3 can be config-

ured with weak pull-ups and also for wake-up on

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

functions are not individually pin selectable. If GP3/

MCLR is configured as MCLR, a weak pull-up can be

enabled via the Configuration Word. Configuring GP3

as MCLR disables the wake-up on change function for

this pin.

5.2

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 corre-

sponding output driver in a High-Impedance mode. A

‘0’ puts the contents of the output data latch on the

selected pins, enabling the output buffer. The excep-

tions are GP3, which is input only, and the GP2/T0CKI/

FOSC4 pin, which may be controlled by various

registers. See Table 5-1.

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

drivers disabled) upon Reset.

5.3

I/O Interfacing

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

Figure 5-1. All port pins, except GP3, 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 GPIO, 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 GP3) can be programmed individually as

input or output.

FIGURE 5-1:

EQUIVALENT CIRCUIT

FOR A SINGLE I/O PIN

TABLE 5-1:

ORDER OF PRECEDENCE FOR PIN FUNCTIONS

TABLE 5-2:

REQUIREMENTS TO MAKE PINS AVAILABLE IN DIGITAL MODE

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.

Data

Bus

Port

TRIS ‘f’

Data

TRIS

RD Port

VSS

VDD

I/O

Reg

Latch

Reset

Note 1:

I/O pins have protection diodes to VDD and

VSS.

See Table 3-1 for buffer type.

VSS

VDD

(2)

(1)

Priority

GP0

GP1

GP2

GP3

AN0

AN1

FOSC4

MCLR

TRIS GPIO

T0CKI

—

TRIS GPIO

—

Bit

GP0

GP1

GP2

GP3

FOSC4

—

T0CS

—

ANS1

—

ANS0

—

MCLRE

—

Legend:

— = Condition of bit will have no effect on the setting of the pin to Digital mode.

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