Microchip Technology IC MCU OTP 2KX PIC17C42A-16/P DIP-40 MCP PIC17C42A-16/P 数据表

 

DS30412C-page 62

 

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 1996 Microchip Technology Inc.

 

9.4.1

PORTE AND DDRE REGISTER

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.        

 

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 9-4 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.

 

MOVLB

1

;  Select Bank 1

CLRF

PORTE

;  Initialize PORTE data

;

latches before setting

;

the data direction

;

register

MOVLW

0x03

;  Value used to initialize

;   data direction

MOVWF

DDRE

;  Set RE<1:0> as inputs

;

RE<2> as outputs

 

;

 

RE<7:3> are always

 

;

 

read as '0'

Note: I/O pins have protection diodes to V

DD

 and Vss.

Q

D

CK

TTL

0

1

Q

D

CK

R

S

Input

Buffer

Port

Data

Data Bus

RD_PORTE

WR_PORTE

RD_DDRE

WR_DDRE

EX_EN

CNTL

DRV_SYS

SYS BUS

Control