參數(shù)資料
型號： PIC16C54C
廠商： Microchip Technology Inc.
英文描述： EPROM/ROM-Based 8-Bit CMOS Microcontroller(18引腳、12個I/O端口、512位EPROM/ROM的8位CMOS微控制器)
中文描述： 存儲器/基于ROM的8位CMOS微控制器（18引腳，12個的I / O，512位存儲器端口/光盤的8位的CMOS微控制器）
文件頁數(shù)： 26/158頁
文件大小： 1194K
代理商： PIC16C54C
PIC16C5X
DS30453C-page 26
Preliminary
2000 Microchip Technology Inc.
5.6
I/O Programming Considerations
5.6.1
BI-DIRECTIONAL I/O PORTS
Some instructions operate internally as read followed
by write operations. The
BCF
and
BSF
instructions, for
example, read the entire port into the CPU, execute the
bit operation and re-write the result. Caution must be
used when these instructions are applied to a port
where one or more pins are used as input/outputs. For
example, a
BSF
operation on bit5 of PORTB will cause
all eight bits of PORTB to be read into the CPU, bit5 to
be set and the PORTB value to be written to the output
latches. If another bit of PORTB is used as a bi-direc-
tional I/O pin (say bit0) and it is defined as an input at
this time, the input signal present on the pin itself would
be read into the CPU and rewritten to the data latch of
this particular pin, overwriting the previous content. As
long as the pin stays in the input mode, no problem
occurs. However, if bit0 is switched into output mode
later on, the content of the data latch may now be
unknown.
Example 5-1 shows the effect of two sequential
read-modify-write instructions (e.g.,
BCF, BSF
, etc.) on
an I/O port.
A pin actively outputting a high or a low should not be
driven from external devices at the same time in order
to change the level on this pin (
“
wired-or
”
,
“
wired-and
”
).
The resulting high output currents may damage the
chip.
EXAMPLE 5-1:
READ-MODIFY-WRITE
INSTRUCTIONS ON AN
I/O PORT
;Initial PORT Settings
; PORTB<7:4> Inputs
; PORTB<3:0> Outputs
;PORTB<7:6> have external pull-ups and are
;not connected to other circuitry
;
; PORT latch PORT pins
; ---------- ----------
BCF PORTB, 7 ;01pp pppp 11pp pppp
BCF PORTB, 6 ;10pp pppp 11pp pppp
MOVLW 03Fh ;
TRIS PORTB ;10pp pppp 10pp pppp
;
;Note that the user may have expected the pin
;values to be 00pp pppp. The 2nd BCF caused
;RB7 to be latched as the pin value (High).
5.6.2
SUCCESSIVE OPERATIONS ON I/O
PORTS
The actual write to an I/O port happens at the end of an
instruction cycle, whereas for reading, the data must be
valid at the beginning of the instruction cycle
(Figure 5-2). Therefore, care must be exercised if a
write followed by a read operation is carried out on the
same I/O port. The sequence of instructions should
allow the pin voltage to stabilize (load dependent)
before the next instruction, which causes that file to be
read into the CPU, is executed. Otherwise, the previous
state of that pin may be read into the CPU rather than
the new state. When in doubt, it is better to separate
these instructions with a
NOP
or another instruction not
accessing this I/O port.
FIGURE 5-2:
SUCCESSIVE I/O OPERATION
PC
PC + 1
PC + 2
PC + 3
Q1
Q2
Q3 Q4
Q1
Q2
Q3 Q4 Q1
Q2 Q3 Q4
Q1
Q2
Q3 Q4
Instruction
fetched
RB<7:0>
MOVWF PORTB
NOP
Port pin
sampled here
NOP
MOVF PORTB,W
Instruction
executed
MOVWF PORTB
(Write to
PORTB)
NOP
MOVF PORTB,W
(Read
PORTB)
This example shows a write
to PORTB followed by a read
from PORTB.
Port pin
written here
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
PIC16C54C/JW 功能描述:8位微控制器 -MCU .75KB 25 RAM 12 I/O RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風(fēng)格:SMD/SMT
PIC16C54C-04/P 功能描述:8位微控制器 -MCU .75KB 25 RAM 12 I/O 4MHz PDIP18 RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風(fēng)格:SMD/SMT
PIC16C54C-04/P 制造商:Microchip Technology Inc 功能描述:IC 8BIT CMOS MCU 16C54 DIP18
PIC16C54C04/SO 制造商:Microchip Technology 功能描述:8 PIC16C 4MHz 18SOIC 制造商:Microchip Technology 功能描述:8 PIC16C 4MHz 18SOIC Bulk
PIC16C54C-04/SO 功能描述:8位微控制器 -MCU .75KB 25 RAM 12 I/O 4MHz SOIC18 RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風(fēng)格:SMD/SMT
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