PIC17C4X Datasheet, PDF (60/240 Pages) Microchip Technology – High-Performance 8-Bit CMOS EPROM/ROM Microcontroller

PIC17C4X
9.4 PORTD and DDRD Registers
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.
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 9-3 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.
EXAMPLE 9-3: INITIALIZING PORTD
MOVLB 1
CLRF PORTD
MOVLW 0xCF
MOVWF DDRD
; Select Bank 1
; Initialize PORTD data
; latches before setting
; the data direction
; register
; Value used to initialize
; data direction
; Set RD<3:0> as inputs
; RD<5:4> as outputs
; RD<7:6> as inputs
FIGURE 9-7: PORTD BLOCK DIAGRAM (IN I/O PORT MODE)
TTL
Input
Buffer
0 ^Port
Data
1
Q
D
CK
to D_Bus → IR
INSTRUCTION READ
Data Bus
RD_PORTD
WR_PORTD
Q
D
CK
RS
Note: I/O pins have protection diodes to VDD and Vss.
RD_DDRD
WR_DDRD
EX_EN
DATA/ADDR_OUT
DRV_SYS
SYS BUS
Control
DS30412C-page 60
© 1996 Microchip Technology Inc.