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Question about ICD-U80 and MCLR pin

 
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Woody



Joined: 11 Sep 2003
Posts: 24
Location: Warmenhuizen - NL

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Question about ICD-U80 and MCLR pin
PostPosted: Sun Feb 16, 2020 11:39 am     Reply with quote

I'm in the middle of a small project with a 16f1509 and running into something I have not seen before. I was wondering if someone found a solution to this.

In this project, all of the 1509's pins are used, which is the reason I'm also using MCLR as an input, just for a simple, on-board calibration switch.

Wired as seen here: https://box.postkamer.eu/cloud/index.php/s/cMmyRP3K4zj6q8W

Now when I connect the ICD_U80 I can program the 1509 without problems. The PIC starts and runs ok.

However, if I leave the ICSP cable connected to the ICD and test the on-board switch, it does not work. I turns out that the ICD keeps the MCLR pin at a 3.8V level, and the switch, via the 5.6k resistor, does not lower this level enough to be seen as 'input'.

Disconnecting the USB cable from the ICD does not help; I have to disconnect the ICSP cabling (just the MCLR wire) to make the switch work. Which is, however small the action, starting to become a bit of a pain in the backside.

So I was wondering, is there a solution to this? Why is the ICD keeping the MCLR pin at a (to me) strange level of 3.8V? Andis there something I should / could have done to prevent this?

Kind regards,


Paul
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