PIC17C752 datasheet(78/306 Pages) MICROCHIP

78 / 306 page

PIC17C7XX

DS30289C-page 78

 1998-2013 Microchip Technology Inc.

10.3

PORTC and DDRC Registers

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

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

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

the DDRC register configures the corresponding port

pin as an output. Reading PORTC reads the status of

the pins, whereas writing to PORTC will write to the port

latch. PORTC is multiplexed with the system bus.

When operating as the system bus, PORTC is the low

order byte of the address/data bus (AD7:AD0). The tim-

ing for the system bus is shown in the Electrical Speci-

fications section.

Example 10-3 shows an instruction sequence to initial-

ize PORTC. 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 10-3:

INITIALIZING PORTC

FIGURE 10-9:

BLOCK DIAGRAM OF RC7:RC0 PORT PINS

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

general purpose I/O.

MOVLB

; Select Bank 1

CLRF

PORTC, F

; Initialize PORTC data

; latches before setting

; the data direction reg

MOVLW

0xCF

; Value used to initialize

; data direction

MOVWF

DDRC

; Set RC<3:0> as inputs

; RC<5:4> as outputs

; RC<7:6> as inputs

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_PORTC

WR_PORTC

RD_DDRC

WR_DDRC

EX_EN

DATA/ADDR_OUT

DRV_SYS

System Bus

Control

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