PIC18F2420/2520/4420/4520
The fourth pin of PORTE (MCLR/VPP/RE3) is an input
only pin. Its operation is controlled by the MCLRE Con-
figuration bit. When selected as a port pin (MCLRE = 0),
10.5 PORTE, TRISE and LATE
Registers
Depending on the particular PIC18F2420/2520/4420/
4520 device selected, PORTE is implemented in two
different ways.
it functions as a digital input only pin; as such, it does not
have TRIS or LAT bits associated with its operation.
Otherwise, it functions as the device’s Master Clear
input. In either configuration, RE3 also functions as the
programming voltage input during programming.
For 40/44-pin devices, PORTE is a 4-bit wide port.
Three pins (RE0/RD/AN5, RE1/WR/AN6 and RE2/CS/
AN7) are individually configurable as inputs or outputs.
These pins have Schmitt Trigger input buffers. When
selected as an analog input, these pins will read as ‘0’s.
Note:
On a Power-on Reset, RE3 is enabled as
digital input only if Master Clear
functionality is disabled.
a
The corresponding Data Direction register is TRISE.
Setting a TRISE bit (= 1) will make the corresponding
PORTE pin an input (i.e., put the corresponding output
driver in a high-impedance mode). Clearing a TRISE bit
(= 0) will make the corresponding PORTE pin an output
(i.e., put the contents of the output latch on the selected
pin).
EXAMPLE 10-5:
INITIALIZING PORTE
CLRF
PORTE
LATE
0Ah
; Initialize PORTE by
; clearing output
; data latches
; Alternate method
; to clear output
; data latches
CLRF
TRISE controls the direction of the RE pins, even when
they are being used as analog inputs. The user must
make sure to keep the pins configured as inputs when
using them as analog inputs.
MOVLW
MOVWF
MOVLW
; Configure A/D
ADCON1 ; for digital inputs
03h
; Value used to
; initialize data
; direction
; Set RE<0> as inputs
; RE<1> as outputs
; RE<2> as inputs
Note:
On a Power-on Reset, RE<2:0> are
configured as analog inputs.
MOVWF
TRISE
The upper four bits of the TRISE register also control
the operation of the Parallel Slave Port. Their operation
is explained in Register 10-1.
10.5.1
PORTE IN 28-PIN DEVICES
For 28-pin devices, PORTE is only available when
Master Clear functionality is disabled (MCLRE = 0). In
these cases, PORTE is a single bit, input only port com-
prised of RE3 only. The pin operates as previously
described.
The Data Latch register (LATE) is also memory
mapped. Read-modify-write operations on the LATE
register, read and write the latched output value for
PORTE.
© 2008 Microchip Technology Inc.
DS39631E-page 117
MICROCHIP [ MICROCHIP ]
