如何保护数字逻辑从VPP驱动MCLR/VPP/RA3引脚

跳线运动员你不能有两个东西驱动同一个PIN。



      以下为原文

    A jumper. You can’t have two things driving the same pin.

两个二极管和一个下拉可以工作。不会很快。请看，D1、D2和R3如何布置在这个示意图上——HTTP://www. NurthnCualas.COM/NSDSP/HVP.HTM-并忽略其他所有内容。



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    Two diodes and a pull-down can work. Won't be fast though. See, how D1, D2 and R3 are arranged on this schematics - http://www.northernsoftware.com/nsdsp/hvp.htm - and disregard everything else.
 

你没有提到你正在使用哪一个PIC。如果是最近的PIC，它将支持低电压编程，这是为了避免这个问题。



      以下为原文

    You did not mention WHICH PIC you are using.
If it is a recent one, it will support low voltage programming, which is designed to avoid precisely this problem.
 

我不知道有任何8引脚PIC微控制器，让我使用LVP，但仍然使用RA3作为输入引脚。



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I wasn't aware that there were any 8-pin PIC microcontrollers that would let me use LVP and yet still use RA3 as an input pin.

10K隔离电阻之间/MCLR（+ICSP VPP）和逻辑驱动它，除非你知道逻辑有一个高侧MOSFET的身体二极管到VDD轨道，肖特基二极管钳位到Vdd在逻辑输出。所有的ICSP能力的微芯片程序员加载VDD足以阻止它上升，如果你我们E 10K隔离电阻器或上拉电阻。它们通常被额定为在VPP上驱动5K负载，但如果低于10K，则不会保持VDD下降。忽略微芯片数据表等，显示470R隔离电阻。N.B.另一个陷阱是PGC（ICSPLK）和PGD（ICSPDAT）的水平。两者都需要低到进入编程模式。如果你在没有隔离电阻GT；1K的情况下驱动它们，或者它们在几百毫秒的功率下被设置为正常的高输出，那么你很可能会遇到问题。…



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    10K isolation resistor between /MCLR (+ICSP Vpp) and logic driving it, and unless you *know* the logic has a high side MOSFET with a body diode going to the Vdd rail, a Schottky diode clamp to Vdd at the logic output.
 
All ICSP capable Microchip programmers load Vdd enough to stop it rising if you use a 10K isolation resistor or pullup.  They are typically rated to drive a 5K load on Vpp, but wont hold Vdd down if you go below 10K.   Ignore Microchip datasheets etc. that shows a 470R isolation resistor.
 
N.B. a further pitfall is the level on PGC (ICSPCLK) and PGD (ICSPDAT).  Both need to be low to enter programming mode.   If you've got something driving them high without isolation resistors >1K or they are set as normally high outputs within a few hundred ms of powerup you are likely to have problems . . .

你说得对。LVP模式防止MCLR被用作我所遇到的所有PIC的通用输入。然而，它总是有助于说明您正在使用的设备。



      以下为原文

   
You're right. LVP mode prevents MCLR being used as a general purpose input on all the PICs I have encountered.
Nevertheless, it's always helpful to state which device you are working with.