PIC16F883 Microchip Technology Inc., PIC16F883 Datasheet - Page 41

• Manufacturer Part Number: PIC16F883
• Description: 28/40/44-pin Flash-based, 8-bit Cmos Microcontrollers With Nanowatt Technology
• Manufacturer: Microchip Technology Inc.

3.0
There are as many as thirty-five 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.
3.1
PORTA is a 8-bit wide, bidirectional port. The
corresponding data direction register is TRISA
(Register 3-2). Setting a TRISA bit (= 1) will make the
corresponding PORTA pin an input (i.e., disable the
output driver). Clearing a TRISA bit (= 0) will make the
corresponding PORTA pin an output (i.e., enables
output driver and puts the contents of the output latch
on the selected pin). Example 3-1 shows how to
initialize PORTA.
Reading the PORTA register (Register 3-1) reads the
status of the pins, whereas writing to it will write to the
PORT latch. All write operations are read-modify-write
REGISTER 3-1:
REGISTER 3-2:
© 2007 Microchip Technology Inc.
bit 7
Legend:
R = Readable bit
-n = Value at POR
bit 7-0
bit 7
Legend:
R = Readable bit
-n = Value at POR
bit 7-0
Note 1:
R/W-1
TRISA7
R/W-x
RA7
I/O PORTS
PORTA and the TRISA Registers
(1)
TRISA<7:6> always reads ‘1’ in XT, HS and LP Oscillator modes.
RA<7:0>: PORTA I/O Pin bit
1 = Port pin is > V
0 = Port pin is < V
TRISA<7:0>: PORTA Tri-State Control bit
1 = PORTA pin configured as an input (tri-stated)
0 = PORTA pin configured as an output
R/W-1
TRISA6
R/W-x
RA6
PORTA: PORTA REGISTER
TRISA: PORTA TRI-STATE REGISTER
(1)
W = Writable bit
‘1’ = Bit is set
W = Writable bit
‘1’ = Bit is set
IH
IL
TRISA5
R/W-x
R/W-1
RA5
PIC16F882/883/884/886/887
TRISA4
R/W-1
R/W-x
RA4
Preliminary
U = Unimplemented bit, read as ‘0’
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared
‘0’ = Bit is cleared
TRISA3
R/W-x
R/W-1
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.
The TRISA register (Register 3-2) controls the PORTA
pin output drivers, even when they are being used as
analog inputs. The user should ensure the bits in the
TRISA register are maintained set when using them as
analog inputs. I/O pins configured as analog input always
read ‘0’.
EXAMPLE 3-1:
RA3
BANKSEL PORTA
CLRF
BANKSEL ANSEL
CLRF
BCF
BANKSEL TRISA
MOVLW
MOVWF
Note:
PORTA
ANSEL
STATUS,RP1 ;Bank 1
0Ch
TRISA
The ANSEL register must be initialized to
configure an analog channel as a digital
input. Pins configured as analog inputs will
read ‘0’.
TRISA2
R/W-1
R/W-x
RA2
INITIALIZING PORTA
;
;Init PORTA
;
;digital I/O
;
;Set RA<3:2> as inputs
;and set RA<5:4,1:0>
;as outputs
x = Bit is unknown
x = Bit is unknown
TRISA1
R/W-1
R/W-x
RA1
DS41291D-page 39
TRISA0
R/W-x
R/W-1
RA0
bit 0
bit 0