PIC17C44 Datasheet, PDF (58/241 Pages) Microchip Technology – High-Performance 8-Bit CMOS EPROM/ROM Microcontroller

PIC17C4X
9.3 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 it 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 timing for
the system bus is shown in the Electrical Characteris-
tics 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 9-2 shows the instruction sequence to initial-
ize PORTC. The Bank Select Register (BSR) must be
selected to Bank 1 for the port to be initialized.
EXAMPLE 9-2: INITIALIZING PORTC
MOVLB 1
CLRF PORTC
MOVLW 0xCF
MOVWF DDRC
; Select Bank 1
; Initialize PORTC data
; latches before setting
; the data direction
; register
; Value used to initialize
; data direction
; Set RC<3:0> as inputs
; RC<5:4> as outputs
; RC<7:6> as inputs
FIGURE 9-6: BLOCK DIAGRAM OF RC<7:0> PORT PINS
TTL
Input
Buffer
0 ^Port
Data
1
Q
D
CK
to D_Bus → IR
INSTRUCTION READ
Data Bus
RD_PORTC
WR_PORTC
Q
D
CK
RS
Note: I/O pins have protection diodes to VDD and Vss.
RD_DDRC
WR_DDRC
EX_EN
DATA/ADDR_OUT
DRV_SYS
SYS BUS
Control
DS30412C-page 58
© 1996 Microchip Technology Inc.