PIC12F629/675
register are maintained set when using them as analog
inputs. I/O pins configured as analog inputs always
read ‘0’.
3.0
GPIO PORT
There are as many as six general purpose I/O pins
available. Depending on which peripherals are
enabled, some or all of the pins may not be available as
general purpose I/O. In general, when a peripheral is
enabled, the associated pin may not be used as a
general purpose I/O pin.
Note: The ANSEL (9Fh) and CMCON (19h)
registers (9Fh) must be initialized to
configure an analog channel as a digital
input. Pins configured as analog inputs will
read ‘0’. The ANSEL register is defined for
the PIC12F675.
Note: Additional information on I/O ports may be
found in the PIC® Mid-Range Reference
Manual, (DS33023).
EXAMPLE 3-1:
INITIALIZING GPIO
BCF
STATUS,RP0
GPIO
07h
CMCON
STATUS,RP0
ANSEL
0Ch
;Bank 0
;Init GPIO
;Set GP<2:0> to
;digital IO
;Bank 1
;Digital I/O
;Set GP<3:2> as inputs
;and set GP<5:4,1:0>
;as outputs
3.1
GPIO and the TRISIO Registers
CLRF
MOVLW
MOVWF
BSF
CLRF
MOVLW
MOVWF
GPIO is an 6-bit wide, bidirectional port. The
corresponding data direction register is TRISIO.
Setting a TRISIO bit (= 1) will make the corresponding
GPIO pin an input (i.e., put the corresponding output
driver in a High-Impedance mode). Clearing a TRISIO
bit (= 0) will make the corresponding GPIO pin an
output (i.e., put the contents of the output latch on the
selected pin). The exception is GP3, which is input-only
and its TRISIO bit will always read as ‘1’. Example 3-1
shows how to initialize GPIO.
TRISIO
3.2
Additional Pin Functions
Every GPIO pin on the PIC12F629/675 has an
interrupt-on-change option and every GPIO pin, except
GP3, has a weak pull-up option. The next two sections
describe these functions.
Reading the GPIO 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.
Therefore, a write to a port implies that the port pins are
read, this value is modified, and then written to the
PORT data latch. GP3 reads ‘0’ when MCLREN = 1.
3.2.1
WEAK PULL-UP
Each of the GPIO pins, except GP3, has an individually
configurable weak internal pull-up. Control bits WPUx
enable or disable each pull-up. Refer to Register 3-3.
Each weak pull-up is automatically turned off when the
port pin is configured as an output. The pull-ups are
disabled on a Power-on Reset by the GPPU bit
(OPTION<7>).
The TRISIO register controls the direction of the
GP pins, even when they are being used as analog
inputs. The user must ensure the bits in the TRISIO
REGISTER 3-1:
GPIO: GPIO REGISTER (ADDRESS: 05h)
U-0
U-0
R/W-x
R/W-x
R/W-x
R/W-x
R/W-x
R/W-x
GPIO5
GPIO4
GPIO3
GPIO2
GPIO1
GPIO0
—
—
bit 7
bit 0
Legend:
R = Readable bit
-n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared x = Bit is unknown
bit 7-6
bit 5-0
Unimplemented: Read as ‘0’
GPIO<5:0>: General Purpose I/O pin
1= Port pin is >VIH
0= Port pin is <VIL
2010 Microchip Technology Inc.
DS41190G-page 21
MICROCHIP [ MICROCHIP ]
