怎么在PIC16F628a上使用MCLR

这里有一些因素需要考虑。在PIC16F628 A上，数据表告诉你thjat MCLR是一个“ST”输入。（表3-2:PIC16F62A/628 A/648 A引脚说明）“电规范”部分告诉您，ST引脚上的有效高输入是“0.8VDD”，因此如果VDD为5.0V，那么您需要至少4V的引脚被认为是一个安全的“高”。ES（在处理器内部），这将限制引脚电压到它自己的VDD加上大约0.3V，所以上拉电阻将不能将引脚拉到大于3.3±0.3＝3.6V。您可以在PI和PIC之间插入串联电阻器，但是您必须确保当皮是拉低，它可以使MCLR引脚低于0.2VDD，这是1V.所以，从470R到1K可能工作。你必须做这些。一个更干净的解决方案是从NPI晶体管的基极从PI驱动，并使其拉低MCLR。（另一个考虑是，PIC16F628 A现在是一个14年的芯片。有PIN兼容PIC16F1XXX芯片，比PIC16F628 A更便宜、更快、更容易编程。



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    There are a few factors to consider here.
On a PIC16F628A, the datasheet tells you thjat MCLR is an "ST" input. ("TABLE 3-2: PIC16F627A/628A/648A PINOUT DESCRIPTION")
The "Electrical Specifications" section tells you that a valid high input on an ST pin is "0.8VDD", so if VDD is 5.0V, then you need at least 4V on the pin to be considered a safe "high".
The PIN ion the RaspBerry Pi will have ESD protection diodes on it (internal to the processor), which will limit the pin voltage to its own VDD plus about 0.3V, so a pullup resistor will not be able to pull the pin to more than 3.3 + 0.3 = 3.6V.
 
You could insert a series resistor between the Pi and the PIC, but you'd have to make sure that when the Pi was pulling low, it could get the MCLR pin down below 0.2VDD which is 1V.
so, something from 470R to 1k might work. You'd have to do the sums.
 
A cleaner solution would be to drive the base of an NPN transistor from the PI, and get that to pull MCLR down.
 
(Another consideration is, the PIC16F628A is a 14 year old chip now. There are pin compatible PIC16F1xxx chips that are cheaper, faster, and easier to program than the PIC16F628A.

Raspberry Pi的IO扩展器可以配置为开路漏输出：HTTPS://引脚。XYZ/引脚/ IoPiPixOn0*各种接口电路：http://www. eluux.Org/rPIG-GPIOI接口电路，单个小型NMOS器件将为任何IO引脚提供开路漏极能力。



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    There is an IO expander for the Raspberry Pi that can be configured for open drain outputs:
 
https://pinout.xyz/pinout/io_pi_zero#
 
Various interface circuits:
 
http://www.elinux.org/RPi_GPIO_Interface_Circuits
 
A single small NMOS device would provide open drain capability to any IO pin.

非常感谢！事实上，QHB所提到的NPN晶体管方法和ELIUX.ORG POST无疑是最好的方法。我知道我有几个2N3904晶体管漂浮在楼下-完美！非常感谢！马歇尔



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    Thanks so much! Actually, the NPN transistor method mentioned by qhb and in the elinux.org post are definitely the best way to go, given my current setup. I know I've got a few 2N3904 transistors floating around downstairs - perfect! Thanks so much!
 
Marshall