PIC17C44-08SLASHP datasheet(60/240 Pages) MICROCHIP

60 / 240 page

PIC17C4X

DS30412C-page 60

9.4

PORTD and DDRD Registers

PORTD is an 8-bit bi-directional port. The correspond-

ing data direction register is DDRD. A '1' in DDRD con-

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

the DDRC register conﬁgures the corresponding port

pin as an output. Reading PORTD reads the status of

the pins, whereas writing to it will write to the port latch.

PORTD is multiplexed with the system bus. When

operating as the system bus, PORTD is the high order

byte of the address/data bus (AD15:AD8). The timing

for the system bus is shown in the Electrical Character-

istics section.

Note:

This port is conﬁgured as the system bus

when the device’s conﬁguration bits are

selected to Microprocessor or Extended

Microcontroller modes. In the two other

microcontroller modes, this port is a gen-

eral purpose I/O.

Example 9-3 shows the instruction sequence to initial-

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

selected to Bank 1 for the port to be initialized.

EXAMPLE 9-3:

INITIALIZING PORTD

MOVLB

;

Select Bank 1

CLRF

PORTD

;

Initialize PORTD data

;

latches before setting

;

the data direction

;

MOVLW

0xCF

;

Value used to initialize

;

data direction

MOVWF

DDRD

;

Set RD<3:0> as inputs

;

RD<5:4> as outputs

;

RD<7:6> as inputs

FIGURE 9-7:

PORTD BLOCK DIAGRAM (IN I/O PORT MODE)

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

TTL

Input

Buffer

Port

Data

to D_Bus

→ IR

INSTRUCTION READ

Data Bus

RD_PORTD

WR_PORTD

RD_DDRD

WR_DDRD

EX_EN

DATA/ADDR_OUT

DRV_SYS

SYS BUS

Control

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