上电复位电路编程

10K是基本电路。如果MCLR是启用的，并且内部上拉不是在芯片中启用或不需要的。附加二极管是为了防止编程电压到达VCC。如果整个电路没有足够的负载以确保Vcc不超过伏特，则需要。CAPS可以帮助EMI问题。当芯片没有内部复位电路时，大多数都是过去的。



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    The 10k is the basic circuit. Needed if mclr is enables and the internal pull-up is not enabled or not in the chip. The addition diode is to prevent the programming voltage from getting to Vcc. Need if the entire circuit does not have enough load to insure Vcc is not over volted. Caps can help EMI problems. Most are hold overs from the past when the chips did not have an internal reset circuit.

所有现有的微芯片程序员从VDDY目标中汲取足够的电流，而不需要在MC/R电路中的二极管来防止VDD上升，只要隔离或上拉电阻器为gt；＝10K。



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    All current Microchip programmers sink enough current from Vdd_target not to need a diode in the /MCLR circuit to prevent Vdd rising, provided the isolation or pullup resistor is >=10K.

我懂了。我经常看到的270欧姆到1K欧姆与MCLR引脚连接在一起？



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    I see. and what about the 270 ohm to 1k ohm that I often see inline with the MCLR pin?

那么，如果启用内部上拉，甚至不需要10K吗？



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    so, is even the 10k not needed if the internal pull-up is enabled?

是的，我们仍然使用旧的电阻器/二极管/电容电路，但实际上，当我制作原型时，我避开二极管。不确定他们的行为如何新的部分，但旧的，那里有一个关键的那个别针。



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    Yep, we still use the old resistor/diode/capacitor circuit, but indeed as I make prototypes I avoid the diode. Not sure how they behave the new parts, but old ones where kinda critical on that pin.

我懂了。网上有没有明确的电路？



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    i see. is there a definitive circuit published online somewhere?

你没有提到你正在使用哪一个PIC。如果没有重置按钮，那么就把10K安装到Vdd上，你就完成了。



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    You have not mentioned which PIC you are working with.
If there's no reset button, then just fit the 10k to Vdd and you're done.
 

基本上，这一个：HTTP://www. McCHIP.COM/FUMMS/FUNDPOST/36429



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    basically, this one:
http://www.microchip.com/forums/FindPost/364291

这是为了限制下冲电流，使得在使用开关产生复位脉冲时不会发生SCR闭锁。基本上，由开关引起的快速过渡从未终止的复位引脚反射产生负脉冲，该脉冲可以超过PIC的锁存电流规格。



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This is to limit the undershoot current so that SCR latchup does not occur when using a switch to generate a reset pulse. Basically, the fast transition caused by a switch reflects from the un-terminated reset pin creating a negative pulse which can exceed the latchup current spec for the PIC

我讨论了重置电路，以及一些旧的错误在一些细节：HTTP://www. McCHIP.COM/FUMMS/M692554.ASPXIT通常不是一个好主意，直接短路电容器与开关，因为高脉冲电流将缩短开关寿命和电容器振铃与环路电感会引起EMI，即使存在足够大的隔离电阻来保护PIC不锁存，EMI也可能对系统的其他部分产生不利影响。



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    I discussed reset circuits, and what is wrong with some of the old ones in some detail at : http://www.microchip.com/forums/m692754.aspx
 
Its not generally a good idea to directly short a capacitor with a switch, as the high impulse current will shorten the switch life and the capacitor ringing with the loop inductance causes EMI that is likely to adversely affect other parts of the system even if there is a large enough isolation resistor to protect the PIC against latchup.

我没有意识到PICS之间存在差异。那是关于什么的？我使用PIC16F18326和PIC18F26K40



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    I didn't realise there was differences required between pics. what is that about?
I am using a PIC16F18326 and a PIC18F26K40
 

正如我所说的，我们对每一个家庭来说都是如此。



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    As I said, we're using the above for every family, still today.

不过，请务必阅读数据表。我最近发现，对于PIC18F23 K22的上拉/MCLR的最低推荐值是15K，而不是10K。



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    Be sure to read the datasheet, though. I recently discovered to my surprise that the lowest recommended value for the pullup on /MCLR for the PIC18F23K22 is 15K, not 10K.

我想你是指数据表图4-2的注释。它几乎完全纯FUD！这与电气规格不一致。/MCLR（RE3）是在复位和I/O引脚模式下的Schmitt触发输入，阈值为0.2x和0.8xVDD（PARAMS D142，D149）。其最大泄漏电流在1uA @ 125℃C（PARAM D155）。在1.8V的LF部分（PARAM D001）的最小操作VDD中，它可以容忍MCLR上拉的下降0.36V，这意味着它不能安全超过360K。即使允许X2安全系数，180K也是40K上限的许多倍。15K的下限同样没有意义，因为图4-2显示了一个RC复位电路，注释2指的是对电容器充电的上拉电阻，但是所要求的隔离电阻是Gt＝1K，没有上限，并且对于C的值没有限制。应该注意的是，如果ICSP连接是对隔离电阻器的电容侧进行的，除非电容器如此小，以致于对于RC复位延迟是无用的，否则编程将失败。因此，隔离电阻提供ESD保护同样是假的。我不知道微芯片在哪里。把这些蹩脚的复位电路拿来。也许他们会让暑期实习生画它们，或者他们会在食堂桌布上画绿色蜡笔，带你的孩子去上班。如果你使用组件值建议，只要你使用一个可以在VPP上处理1K隔离电阻负载的生产程序，至少这个功能会起作用。



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    I assume you mean the notes on datasheet Figure 4-2.  IMHO its nearly entirely pure FUD!

This is inconsistent with the electrical specs.  /MCLR (RE3) is a Schmitt trigger input in both reset and I/O pin modes, with thresholds of 0.2x and 0.8x Vdd (params D142, D149).  Its max leakage current in 1uA @125 deg C (param D155).  At minimum operating Vdd for the LF part of 1.8V (param D001), it can therefore tolerate a drop of 0.36V across the MCLR pullup, which means it cant safely exceed 360K.  Even allowing x2 factor of safety, 180K is many times the 40K upper limit suggested.   The lower limit of 15K is equally meaningless as Fig 4-2 shows a RC reset circuit, with note 2 referring to the pullup resistor charging the capacitor, but the isolation resistor called for is >=1K with no upper limit given, and there are no limits suggewsted for the value of C.  Furthermore it should be noted that if the ICSP connection is made to the capacitor side of the isolation resistor, programming will fail unless the capacitor is so small as to be useless for a RC reset delay, so the claim the isolation resisor provides ESD protection is equally bogus.
 
 
I don't know where Microchip get these crappy reset circuits from.  Maybe they get the summer interns to draw them, or maybe they get drawn in green crayon on the canteen tablecloths on bring your kid to work day! 
 
At least this one will actually function if you slavishly follow the component value suggestions, as long as you are using a production programmer that can handle a 1K isolation resistor load on Vpp.