PIC16F628-20P Datasheet, PDF (31/170 Pages) Microchip Technology – FLASH-Based 8-Bit CMOS Microcontroller

5.0 I/O PORTS
The PIC16F62X have two ports, PORTA and PORTB.
Some pins for these I/O ports are multiplexed with an
alternate function for the peripheral features on the
device. In general, when a peripheral is enabled, that
pin may not be used as a general purpose I/O pin.
5.1 PORTA and TRISA Registers
PORTA is an 8-bit wide latch. RA4 is a Schmitt Trigger
input and an open drain output. Port RA4 is multiplexed
with the T0CKI clock input. RA5 is a Schmitt Trigger
input only and has no output drivers. 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 configure these pins as input or
output.
A '1' in the TRISA register puts the corresponding out-
put 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.
The PORTA pins are multiplexed with comparator and
voltage reference functions. The operation of these
pins are selected by control bits in the CMCON
(comparator control register) register and the VRCON
(voltage reference control register) register. When
selected as a comparator input, these pins will read
as '0's.
Note:
RA5 shares function with VPP. When VPP
voltage levels are applied to RA5, the
device will enter Programming mode.
PIC16F62X
Note 1: On RESET, the TRISA register is set to all
inputs. The digital inputs are disabled and
the comparator inputs are forced to
ground to reduce current consumption.
2: TRISA<6:7> is overridden by oscillator
configuration. When PORTA<6:7> is
overridden, the data reads ‘0’ and the
TRISA<6:7> bits are ignored.
TRISA controls the direction of the RA pins, even when
they are being used as comparator inputs. The user
must make sure to keep the pins configured as inputs
when using them as comparator inputs.
The RA2 pin will also function as the output for the
voltage reference. When in this mode, the VREF pin is a
very high impedance output. The user must configure
TRISA<2> bit as an input and use high impedance
loads.
In one of the Comparator modes defined by the
CMCON register, pins RA3 and RA4 become outputs
of the comparators. The TRISA<4:3> bits must be
cleared to enable outputs to use this function.
EXAMPLE 5-1: Initializing PORTA
CLRF PORTA
;Initialize PORTA by
;setting output data latches
MOVLW 0x07
;Turn comparators off and
MOVWF CMCON
;enable pins for I/O
;functions
BCF STATUS, RP1
BSF STATUS, RP0;Select Bank1
MOVLW 0x1F
;Value used to initialize
;data direction
MOVWF TRISA
;Set RA<4:0> as inputs
;TRISA<5> always
;read as ‘1’.
;TRISA<7:6>
;depend on oscillator mode
 2003 Microchip Technology Inc.
Preliminary
DS40300C-page 29