PIC16C620 Microchip Technology, PIC16C620 Datasheet - Page 25

• Manufacturer Part Number: PIC16C620
• Description: EPROM-Based 8-Bit CMOS Microcontroller
• Manufacturer: Microchip Technology

5.0
The PIC16C62X have two ports, PORTA and PORTB.
5.1
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
FIGURE 5-1:
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.
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.
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.
WR
TRISA
Data
bus
WR
PortA
1998 Microchip Technology Inc.
Note: I/O pins have protection diodes to V
RD PORTA
I/O PORTS
PORTA and TRISA Registers
To Comparator
TRIS Latch
D
D
Data Latch
CK
CK
RD TRISA
BLOCK DIAGRAM OF
RA1:RA0 PINS
Q
Q
Q
Q
Input Mode
Schmitt Trigger
Analog
Q
Input Buffer
EN
V
V
P
N
D
DD
SS
DD
and V
I/O Pin
SS
.
Preliminary
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 V
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:
CLRF
MOVLW 0X07
MOVWF CMCON
BSF
MOVLW 0x1F
MOVWF TRISA
FIGURE 5-2:
Data
bus
WR
PortA
WR
TRISA
Note:
Note: I/O pins have protection diodes to V
RD PORTA
PORTA
STATUS, RP0 ;Select Bank1
To Comparator
D
D
TRIS Latch
Data Latch
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 excess current consumption.
CK
CK
V
RD TRISA
V
ROE
REF
BLOCK DIAGRAM OF RA2 PIN
Q
Q
Q
Q
INITIALIZING PORTA
;Initialize PORTA by setting
;output data latches
;Turn comparators off and
;enable pins for I/O
;functions
;Value used to initialize
;data direction
;Set RA<4:0> as inputs
;TRISA<7:5> are always
;read as '0'.
Input Mode
PIC16C62X
Schmitt Trigger
Analog
Q
Input Buffer
EN
V
V
P
N
D
DS30235G-page 25
DD
SS
DD
REF
and V
RA2 Pin
pin is a
SS
.