PIC17C42 Microchip Technology, PIC17C42 Datasheet - Page 62

• Manufacturer Part Number: PIC17C42
• Description: High-Performance 8-Bit CMOS EPROM/ROM Microcontroller
• Manufacturer: Microchip Technology

PIC17C4X
9.4.1
PORTE is a 3-bit bi-directional port. The corresponding
data direction register is DDRE. A '1' in DDRE config-
ures the corresponding port pin as an input. A '0' in the
DDRE register configures the corresponding port pin
as an output. Reading PORTE reads the status of the
pins, whereas writing to it will write to the port latch.
PORTE is multiplexed with the system bus. When
operating as the system bus, PORTE contains the con-
trol signals for the address/data bus (AD15:AD0).
These control signals are Address Latch Enable (ALE),
Output Enable (OE), and Write (WR). The control sig-
nals OE and WR are active low signals. The timing for
the system bus is shown in the Electrical Characteris-
tics section.
FIGURE 9-8:
DS30412C-page 62
Note: I/O pins have protection diodes to V
Note:
PORTE AND DDRE REGISTER
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.
PORTE BLOCK DIAGRAM (IN I/O PORT MODE)
TTL
Input
Buffer
0
1
Data
Port
DD
and Vss.
R
Q
Q
CK
CK
S
D
D
Example 9-4 shows the instruction sequence to initial-
ize PORTE. The Bank Select Register (BSR) must be
selected to Bank 1 for the port to be initialized.
EXAMPLE 9-4:
MOVLB 1
CLRF
MOVLW 0x03
MOVWF DDRE
PORTE
INITIALIZING PORTE
;
;
;
;
;
;
;
;
;
;
;
Select Bank 1
Initialize PORTE data
Value used to initialize
Set RE<1:0> as inputs
1996 Microchip Technology Inc.
data direction
latches before setting
the data direction
register
RE<2> as outputs
RE<7:3> are always
read as '0'
WR_PORTE
RD_PORTE
WR_DDRE
RD_DDRE
DRV_SYS
Data Bus
EX_EN
CNTL
SYS BUS
Control