Datasheet

PIC17C4X
DS30412C-page 58  1996 Microchip Technology Inc.
9.3 POR
TC 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 ; Select Bank 1
CLRF PORTC ; Initialize PORTC data
; latches before setting
; the data direction
; register
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
FIGURE 9-6: BLOCK DIAGRAM OF RC<7:0> PORT PINS
Note: I/O pins have protection diodes to VDD 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_PORTC
WR_PORTC
RD_DDRC
WR_DDRC
EX_EN
DATA/ADDR_OUT
DRV_SYS
SYS BUS
Control