參數資料
型號： PIC16C642
廠商： Microchip Technology Inc.
英文描述： 8-Bit EPROM Microcontrollers with Analog Comparators(每個I/O口有25mA驅動/吸收電流，可編程Vref，微控制器)
中文描述： 8位EPROM微控制器與模擬比較器（每個的I / O口有25毫安驅動/吸收電流，可編程Vref的，微控制器）
文件頁數： 38/136頁
文件大?。?/td> 837K
代理商： PIC16C642
PIC16C64X & PIC16C66X
DS30559A-page 38
Preliminary
1996 Microchip Technology Inc.
5.6
I/O Programming Considerations
5.6.1
BI-DIRECTIONAL I/O PORTS
Any instruction which writes, operates internally as a
read followed by a write operation. The
BCF
and
BSF
instructions, for example, read the register into the
CPU, execute the bit operation and write the result
back to the register. Caution must be used when these
instructions are applied to a port with both inputs and
outputs defined. For example, a
BSF
operation on bit5
of PORTB will cause all eight bits of PORTB to be read
into the CPU. Then the
BSF
operation takes place on
bit5 and PORTB is written to the output latches. If
another bit of PORTB is used as a bi-directional I/O pin
(e.g., 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.
Reading the port register reads the values of the port
pins. Writing to the port register writes the value to the
port latch. When using read-modify-write instructions
(e.g.,
BCF, BSF
, etc.) on a port, the value of the port
pins is read, the desired operation is done to this value,
and this value is then written to the port latch.
Example 5-4 shows the effect of two sequential
read-modify-write instructions on an I/O port.
A pin actively outputting a Low or High 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 5-4:
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
BCF STATUS, RP1 ;
BSF STATUS, RP0 ;
BCF TRISB, 7 ; 10pp pppp 11pp pppp
BCF TRISB, 6 ; 10pp pppp 10pp pppp
;
;Note that the user may have expected the
;pin values to be 00pp ppp. 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 5-11). 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 be
such to 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 an NOP or another
instruction not accessing this I/O port.
FIGURE 5-11: 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
InstructPC
fetched
RB7:RB0
MOVWF PORTB
write to
PORTB
NOP
Port pin
sampled here
NOP
MOVF PORTB,W
Instruction
executed
MOVWF PORTB
write to
PORTB
NOP
MOVF PORTB,W
T
PD
Note:
This example shows a write to PORTB
followed by a read from PORTB.
Note that:
data setup time = (0.25T
CY
- T
PD
)
where T
CY
= instruction cycle
T
PD
= propagation delay
Therefore, at higher clock frequencies,
a write followed by a read may be
problematic.
相關PDF資料
PDF描述
PIC16C64A Using the 8-Bit Parallel Slave Port(每個I/O口有25mA驅動/吸收電流,并行從動口,1路捕捉/比較/PWM的微控制器)
PIC16C66 8-Bit CMOS Microcontrollers(每個I/O口有25mA驅動/吸收電流,1路捕捉/比較/PWM的微控制器)
PIC16C67 8-Bit CMOS Microcontrollers(每個I/O口有25mA驅動/吸收電流,1路捕捉/比較/PWM的微控制器)
PIC16C62 8-Bit CMOS Microcontrollers(每個I/O口有25mA驅動/吸收電流,22個I/O,2.5V的微控制器)
PIC16C62A 8-Bit CMOS Microcontrollers(每個I/O口有25mA驅動/吸收電流,22個I/O,2.5V的微控制器)
相關代理商/技術參數
參數描述
PIC16C642/JW 功能描述:8位微控制器 -MCU 7KB 176 RAM 22 I/O RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數據總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數據 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 安裝風格:SMD/SMT
PIC16C642-04/SO 功能描述:8位微控制器 -MCU 7KB 176 RAM 22 I/O RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數據總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數據 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 安裝風格:SMD/SMT
PIC16C642-04/SP 功能描述:8位微控制器 -MCU 7KB 176 RAM 22 I/O RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數據總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數據 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 安裝風格:SMD/SMT
PIC16C642-04E/SO 功能描述:8位微控制器 -MCU 7KB 176 RAM 22 I/O RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數據總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數據 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 安裝風格:SMD/SMT
PIC16C642-04E/SP 功能描述:8位微控制器 -MCU 7KB 176 RAM 22 I/O RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數據總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數據 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 安裝風格:SMD/SMT
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