PIC18F2450/4450
When enabling peripheral functions on PORTC pins
other than RC4 and RC5, care should be taken in
defining the TRIS bits. Some peripherals override the
TRIS bit to make a pin an output, while other
peripherals override the TRIS bit to make a pin an
input. The user should refer to the corresponding
peripheral section for the correct TRIS bit settings.
9.3
PORTC, TRISC and LATC
Registers
PORTC is
a 7-bit wide, bidirectional port. The
corresponding data direction register is TRISC. Setting
a TRISC bit (= 1) will make the corresponding PORTC
pin an input (i.e., put the corresponding output driver in
a high-impedance mode). Clearing a TRISC bit (= 0)
will make the corresponding PORTC pin an output (i.e.,
put the contents of the output latch on the selected pin).
Note:
On a Power-on Reset, these pins, except
RC4 and RC5, are configured as digital
inputs. To use pins RC4 and RC5 as
digital inputs, the USB module must be
disabled (UCON<3> = 0) and the on-chip
USB transceiver must be disabled
(UCFG<3> = 1).
In PIC18F2450/4450 devices, the RC3 pin is not
implemented.
The Data Latch register (LATC) is also memory
mapped. Read-modify-write operations on the LATC
register read and write the latched output value for
PORTC.
The contents of the TRISC register are affected by
peripheral overrides. Reading TRISC always returns
the current contents, even though a peripheral device
may be overriding one or more of the pins.
PORTC is primarily multiplexed with serial
communication modules, including the EUSART and
the USB module (Table 9-5). Except for RC4 and RC5,
PORTC uses Schmitt Trigger input buffers.
EXAMPLE 9-3:
INITIALIZING PORTC
Pins RC4 and RC5 are multiplexed with the USB
module. Depending on the configuration of the module,
they can serve as the differential data lines for the on-
chip USB transceiver, or the data inputs from an
external USB transceiver. Both RC4 and RC5 have
TTL input buffers instead of the Schmitt Trigger buffers
on the other pins.
CLRF
PORTC
LATC
07h
; Initialize PORTC by
; clearing output
; data latches
; Alternate method
; to clear output
; data latches
; Value used to
; initialize data
; direction
CLRF
MOVLW
MOVWF
Unlike other PORTC pins, RC4 and RC5 do not have
TRISC bits associated with them. As digital ports, they
can only function as digital inputs. When configured for
USB operation, the data direction is determined by the
configuration and status of the USB module at a given
time. If an external transceiver is used, RC4 and RC5
always function as inputs from the transceiver. If the
on-chip transceiver is used, the data direction is
determined by the operation being performed by the
module at that time.
TRISC
; RC<5:0> as outputs
; RC<7:6> as inputs
When the external transceiver is enabled, RC2 also
serves as the output enable control to the transceiver.
Additional information on configuring USB options is
provided in Section 14.2.2.2 “External Transceiver”.
DS39760A-page 104
Advance Information
© 2006 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
