PIC18F2480 MICROCHIP [Microchip Technology], PIC18F2480 Datasheet - Page 131

• Manufacturer Part Number: PIC18F2480
• Description: 28/40/44-Pin Enhanced Flash Microcontrollers with ECAN Technology, 10-Bit A/D and nanoWatt Technology
• Manufacturer: MICROCHIP [Microchip Technology]

10.0
Depending on the device selected and features
enabled, there are up to five ports available. Some pins
of the I/O ports are multiplexed with an alternate
function from 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.
Each port has three registers for its operation. These
registers are:
• TRIS register (data direction register)
• PORT register (reads the levels on the pins of the
• LAT register (output latch)
The Data Latch register (LAT) is useful for read-modify-
write operations on the value that the I/O pins are
driving.
A simplified model of a generic I/O port, without the
interfaces to other peripherals, is shown in Figure 10-1.
FIGURE 10-1:
 2004 Microchip Technology Inc.
device)
Note 1:
RD LAT
Data
Bus
WR LAT
or Port
WR TRIS
RD TRIS
RD Port
I/O PORTS
I/O pins have diode protection to V
TRIS Latch
Data Latch
D
D
CK
CK
GENERIC I/O PORT
OPERATION
Q
Q
Q
EN
EN
D
DD
and V
PIC18F2480/2580/4480/4580
I/O pin
Buffer
Input
SS
.
(1)
Preliminary
10.1
PORTA is an 8-bit wide, bidirectional port. The corre-
sponding data direction register is TRISA. Setting a
TRISA bit (= 1) will make the corresponding PORTA pin
an input (i.e., put the corresponding output driver in a
high-impedance mode). Clearing a TRISA bit (= 0) will
make the corresponding PORTA pin an output (i.e., put
the contents of the output latch on the selected pin).
Reading the PORTA register reads the status of the
pins, whereas writing to it, will write to the port latch.
The Data Latch register (LATA) is also memory
mapped. Read-modify-write operations on the LATA
register read and write the latched output value for
PORTA.
The RA4 pin is multiplexed with the Timer0 module
clock input to become the RA4/T0CKI pin. Pins RA6
and RA7 are multiplexed with the main oscillator pins;
they are enabled as oscillator or I/O pins by the selec-
tion of the main oscillator in Configuration Register 1H
(see Section 24.1 “Configuration Bits” for details).
When they are not used as port pins, RA6 and RA7 and
their associated TRIS and LAT bits are read as ‘0’.
The other PORTA pins are multiplexed with analog
inputs, the analog V
comparator voltage reference output. The operation of
pins RA3:RA0 and RA5 as A/D converter inputs is
selected by clearing/setting the control bits in the
ADCON1 register (A/D Control Register 1).
All other PORTA pins have TTL input levels and full
CMOS output drivers.
The TRISA register controls the direction of the RA
pins, even when they are being used as analog inputs.
The user must ensure the bits in the TRISA register are
maintained set when using them as analog inputs.
EXAMPLE 10-1:
CLRF
CLRF
MOVLW
MOVWF
MOVWF
MOVWF
MOVLW
MOVWF
Note:
PORTA, TRISA and LATA Registers
PORTA
LATA
0Fh
ADCON1 ; for digital inputs
07h
CMCON
0CFh
TRISA
On a Power-on Reset, RA5 and RA3:RA0
are configured as analog inputs and read
as ‘0’. RA4 is configured as a digital input.
; Initialize PORTA by
; clearing output
; data latches
; Alternate method
; to clear output
; data latches
; Configure A/D
; Configure comparators
; for digital input
; Value used to
; initialize data
; direction
; Set RA<3:0> as inputs
; RA<5:4> as outputs
REF
INITIALIZING PORTA
+ and V
REF
DS39637A-page 129
- inputs and the