参数资料
型号: PIC17CXX
厂商: Microchip Technology Inc.
英文描述: EPROM Memory Programming Specification
中文描述: EPROM存储器编程规范
文件页数: 59/71页
文件大小: 1173K
代理商: PIC17CXX
PIC17C4X
DS30412C-page 62
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 cong-
ures the corresponding port pin as an input. A '0' in the
DDRE register congures 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.
Note:
This port is congured as the system bus
when the device’s conguration 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.
EXAMPLE 9-4:
INITIALIZING PORTE
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'
FIGURE 9-8:
PORTE BLOCK DIAGRAM (IN I/O PORT MODE)
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
Data Bus
RD_PORTE
WR_PORTE
RD_DDRE
WR_DDRE
EX_EN
CNTL
DRV_SYS
SYS BUS
Control
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