參數(shù)資料
型號: pic16c621a
廠商: Microchip Technology Inc.
英文描述: EPROM-Based 8-Bit CMOS Microcontroller(8位CMOS微控制器)
中文描述: 存儲器為基礎(chǔ)的8位CMOS微控制器(8位的CMOS微控制器)
文件頁數(shù): 25/112頁
文件大?。?/td> 1205K
代理商: PIC16C621A
1997 Microchip Technology Inc.
Preliminary
DS30235F-page 25
PIC16C62X(A)
5.0
I/O PORTS
The PIC16C62X(A) have two ports, PORTA and PORTB.
Some pins for these I/O ports are multiplexed with an
alternate function for the peripheral features on the
device. In general, when a peripheral is enabled, that
pin may not be used as a general purpose I/O pin.
5.1
PORTA and TRISA Registers
PORTA is a 5-bit wide latch. RA4 is a Schmitt Trigger input
and an open drain output. Port RA4 is multiplexed with the
T0CKI clock input. All other RA port pins have Schmitt
Trigger input levels and full CMOS output drivers. All pins
have data direction bits (TRIS registers) which can config-
ure these pins as input or output.
A '1' in the TRISA register puts the corresponding output
driver in a hi- impedance mode. A '0' in the TRISA register
puts the contents of the output latch on the selected pin(s).
Reading the PORTA register reads the status of the pins
whereas writing to it will write to the port latch. All write
operations are read-modify-write operations. So a write
to a port implies that the port pins are first read, then this
value is modified and written to the port data latch.
The PORTA pins are multiplexed with comparator and
voltage reference functions. The operation of these
pins are selected by control bits in the CMCON
(comparator control register) register and the VRCON
(voltage reference control register) register. When
selected as a comparator input, these pins will read
as '0's.
FIGURE 5-1:
BLOCK DIAGRAM OF
RA1:RA0 PINS
Note: I/O pins have protection diodes to V
DD
and V
SS
.
Data
bus
Q
D
Q
CK
P
N
WR
PortA
WR
TRISA
Data Latch
TRIS Latch
RD TRISA
RD PORTA
Analog
V
SS
V
DD
I/O Pin
Q
D
Q
CK
Input Mode
D
Q
EN
To Comparator
Schmitt Trigger
Input Buffer
TRISA controls the direction of the RA pins, even when
they are being used as comparator inputs. The user
must make sure to keep the pins configured as inputs
when using them as comparator inputs.
The RA2 pin will also function as the output for the
voltage reference. When in this mode, the V
REF
pin is a
very high impedance output. The user must configure
TRISA<2> bit as an input and use high impedance
loads.
In one of the comparator modes defined by the
CMCON register, pins RA3 and RA4 become outputs
of the comparators. The TRISA<4:3> bits must be
cleared to enable outputs to use this function.
EXAMPLE 5-1:
CLRF
PORTA
INITIALIZING PORTA
;Initialize PORTA by setting
;output data latches
;Turn comparators off and
;enable pins for I/O
;functions
STATUS, RP0 ;Select Bank1
MOVLW 0x1F
;Value used to initialize
;data direction
MOVWF TRISA
;Set RA<4:0> as inputs
;TRISA<7:5> are always
;read as '0'.
FIGURE 5-2:
Data
bus
BLOCK DIAGRAM OF RA2 PIN
Note:
On reset, the TRISA register is set to all
inputs. The digital inputs are disabled and
the comparator inputs are forced to ground
to reduce excess current consumption.
MOVLW 0X07
MOVWF CMCON
BSF
Note: I/O pins have protection diodes to V
DD
and V
SS
.
Q
D
Q
CK
P
N
WR
PortA
WR
TRISA
Data Latch
TRIS Latch
RD TRISA
RD PORTA
Analog
V
SS
V
DD
RA2 Pin
Q
D
Q
CK
Input Mode
D
Q
EN
To Comparator
Schmitt Trigger
Input Buffer
V
ROE
V
REF
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