Microchip Technology IC MCU OTP 2KX PIC17C42A-16/P DIP-40 MCP PIC17C42A-16/P Data Sheet

 

DS30412C-page 60

 



 

 1996 Microchip Technology Inc.

 

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.      

 

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.

 

MOVLB

1

;  Select Bank 1

CLRF

PORTD

;  Initialize PORTD data

;

latches before setting

;

the data direction

;

register

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

Note: I/O pins have protection diodes to V

DD

 and Vss.

Q

D

CK

TTL

0

1

Q

D

CK

R

S

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