PIC17C4X
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.
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.
EXAMPLE 9-2: INITIALIZING PORTC
MOVLB
CLRF
1
;
;
;
;
;
;
;
;
;
;
Select Bank 1
PORTC
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
MOVLW 0xCF
MOVWF DDRC
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.
FIGURE 9-6: BLOCK DIAGRAM OF RC<7:0> PORT PINS
to D_Bus → IR
INSTRUCTION READ
Data Bus
TTL
Input
Buffer
RD_PORTC
WR_PORTC
Port
D
D
0
1
Q
Data
CK
RD_DDRC
WR_DDRC
Q
R
CK
S
EX_EN
DATA/ADDR_OUT
DRV_SYS
SYS BUS
Control
Note: I/O pins have protection diodes to VDD and Vss.
DS30412C-page 58
1996 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
