參數(shù)資料
型號： PIC18F452-I/ML
廠商： Microchip Technology
文件頁數(shù)： 71/134頁
文件大?。?/td> 0K
描述： IC MCU FLASH 16KX16 A/D 44QFN
產(chǎn)品培訓(xùn)模塊： Asynchronous Stimulus
8-bit PIC® Microcontroller Portfolio
標(biāo)準(zhǔn)包裝： 45
系列： PIC® 18F
核心處理器： PIC
芯體尺寸： 8-位
速度： 40MHz
連通性： I²C，SPI，UART/USART
外圍設(shè)備： 欠壓檢測/復(fù)位，LVD，POR，PWM，WDT
輸入/輸出數(shù)： 34
程序存儲器容量： 32KB（16K x 16）
程序存儲器類型： 閃存
EEPROM 大小： 256 x 8
RAM 容量： 1.5K x 8
電壓 - 電源 (Vcc/Vdd)： 4.2 V ~ 5.5 V
數(shù)據(jù)轉(zhuǎn)換器： A/D 8x10b
振蕩器型： 外部
工作溫度： -40°C ~ 85°C
封裝/外殼： 44-VQFN 裸露焊盤
包裝： 管件
配用： XLT44QFN2-ND - SOCKET TRAN ICE 44QFN/40DIP
444-1001-ND - DEMO BOARD FOR PICMICRO MCU
1997 Microchip Technology Inc.
DS30444E - page 41
PIC16C9XX
5.8
I/O Programming Considerations
5.8.1
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 dened. 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 dened 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 contents
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
(ex. BCF, BSF) 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 5-8 shows the effect of two sequential
read-modify-write instructions on an I/O port.
EXAMPLE 5-8:
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).
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.
5.8.2
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 depen-
dent) before the next instruction which causes that le
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 5-11: 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
Instruction
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
PC
TPD
Note:
This example shows a write to PORTB
followed by a read from PORTB.
Note that:
data setup time = (0.25TCY - TPD)
where TCY = instruction cycle
TPD = propagation delay
Therefore, at higher clock frequencies,
a write followed by a read may be prob-
lematic.
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
PIC18F452IPT 制造商:Microchip Technology Inc 功能描述:
PIC18F452T-E/ML 功能描述:8位微控制器 -MCU 40MHz 16KB Flash 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
PIC18F452T-I/L 功能描述:8位微控制器 -MCU 32KB 1536 RAM 34I/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
PIC18F452T-I/ML 功能描述:8位微控制器 -MCU 32KB 1536 RAM 34I/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
PIC18F452T-I/PT 功能描述:8位微控制器 -MCU 32KB 1536 RAM 34I/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
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