Datasheet

© 2009 Microchip Technology Inc. DS39689F-page 123
PIC18F2221/2321/4221/4321 FAMILY
11.5 PORTE, TRISE and LATE
Registers
Depending on the particular PIC18F2221/2321/4221/
4321 family device selected, PORTE is implemented in
two different ways.
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 analog inputs, these pins will read as ‘0’.
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).
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.
The upper four bits of the TRISE register also control
the operation of the Parallel Slave Port. Their operation
is explained in Register 11-1.
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.
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),
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.
EXAMPLE 11-5: INITIALIZING PORTE
11.5.1 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
comprised of RE3 only. The pin operates as previously
described.
Note: On a Power-on Reset, RE<2:0> are
configured as analog inputs.
Note: On a Power-on Reset, RE3 is enabled as
a digital input only if Master Clear
functionality is disabled.
CLRF PORTE ; Initialize PORTE by
; clearing output
; data latches
CLRF LATE ; Alternate method
; to clear output
; data latches
MOVLW 0Fh ; Configure A/D
MOVWF ADCON1 ; for digital inputs
MOVLW 03h ; Value used to
; initialize data
; direction
MOVWF TRISE ; Set RE<0> as inputs
; RE<1> as outputs
; RE<2> as inputs