PIC17C752-08SLASHCL datasheet(80/328 Pages) MICROCHIP

80 / 328 page

PIC17C7XX

DS30289A-page 80

10.5

PORTE and DDRE Register

PORTE is a 4-bit bi-directional port. The corresponding

data direction register is DDRE. A '1' in DDRE conﬁg-

ures the corresponding port pin as an input. A '0' in the

DDRE register conﬁgures the corresponding port pin

as an output. Reading PORTE reads the status of the

pins, whereas writing to PORTE will write to the port

latch. PORTE is multiplexed with the system bus.

When operating as the system bus, PORTE contains

the

control

signals

for

the

address/data

bus

(AD15:AD0). These control signals are Address Latch

Enable (ALE), Output Enable (OE), and Write (WR).

The control signals OE and WR are active low signals.

The timing for the system bus is shown in the Electrical

Speciﬁcations section.

Note:

Three pins of this port are conﬁgured as

the system bus when the device’s conﬁgu-

ration bits are selected to Microprocessor

or Extended Microcontroller modes. The

other pin is a general purpose I/O or

Capture4 pin. In the two other microcon-

troller modes, RE2:RE0 are general pur-

pose I/O pins.

Example 10-5 shows an instruction sequence to initial-

ize PORTE. The Bank Select Register (BSR) must be

selected to Bank 1 for the port to be initialized. The fol-

lowing example uses the MOVLB instruction to load the

BSR register for bank selection.

EXAMPLE 10-5: INITIALIZING PORTE

MOVLB

; Select Bank 1

CLRF

PORTE, F

; Initialize PORTE data

; latches before setting

; the data direction

; register

MOVLW

0x03

; Value used to initialize

; data direction

MOVWF

DDRE

; Set RE<1:0> as inputs

; RE<3:2> as outputs

; RE<7:4> are always

; read as '0'

FIGURE 10-11: BLOCK DIAGRAM OF RE2:RE0 (IN I/O PORT MODE)

Note: I/O pins have protection diodes to VDD and Vss.

TTL

Input

Buffer

Port

Data

Data Bus

RD_PORTE

WR_PORTE

RD_DDRE

WR_DDRE

EX_EN

CNTL

DRV_SYS

SYS BUS

Control

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