PIC17C752-08SLASHCL datasheet(78/328 Pages) MICROCHIP

78 / 328 page

PIC17C7XX

DS30289A-page 78

10.4

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 DDRD register conﬁgures the corresponding port

pin as an output. Reading PORTD reads the status of

the pins, whereas writing to PORTD 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

Speciﬁcations 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 10-4 shows an instruction sequence to initial-

ize PORTD. 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 10-4: INITIALIZING PORTD

MOVLB

; Select Bank 1

CLRF

PORTD, F

; Initialize PORTD data

; latches before setting

; the data direction reg

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 10-10: BLOCK DIAGRAM OF RD7:RD0 PORT PINS (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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