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Author Topic: ICSP with MP monitoring  (Read 1243 times)
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metal
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« on: January 28, 2021, 02:31:28 14:31 »

Hi,

I m unsure if this will work OK for PICs, what do guys think?
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Old_but_Alive
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« Reply #1 on: January 28, 2021, 02:49:11 14:49 »

depends on whats connected to mclr, PGC, PGD.

I would connect a 10K between the pins and the rest of the cicruit unless they are outputs.
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Sideshow Bob
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« Reply #2 on: January 28, 2021, 04:10:46 16:10 »

This is what you can do if you want to more safe than sorry
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metal
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« Reply #3 on: January 29, 2021, 05:07:42 17:07 »

depends on whats connected to mclr, PGC, PGD.

I would connect a 10K between the pins and the rest of the cicruit unless they are outputs.

Nothing is connected to these pins other than the one I have shown in the 1st post.
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dennis78
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« Reply #4 on: January 29, 2021, 10:41:44 22:41 »

I don't work with PICs (and not plan forever Smiley ), but If I remember PICs use about 13V on MCLR pin to enter(or all time during programming) in programming mode.
In this case:

1. reset circuit possible can limit this voltage to Vcc+Vd(due to protection diode or because it exceed absolute maximum voltage ratings conditions if protection diodes not exist)
2.R2 also can limit voltage programming -> you can expect problems during ICSP.

In this situation I will add resistor between \RESET output and MCLR pin on mcu (possible>=10k it depend what is PIC programmer current capability on output for MCLR, maybe 1k is enough?). Maybe this will not work for >10k values in normal reset situation if PIC have internal pull up for MCLR pin, but you must read docs and chose good value.

« Last Edit: January 29, 2021, 10:59:26 22:59 by dennis78 » Logged
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« Reply #5 on: January 29, 2021, 11:13:08 23:13 »


Hello,

it seens that the APX8035 has an O.C.-Output.
I would assume that this will work.
But You should check the maximum ratiings of this output.


Best Regards
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dennis78
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« Reply #6 on: January 29, 2021, 11:39:59 23:39 »

O.C. output isn't guarantee that protection diodes don't exist.

Absoulte max ratings for reset output = 6V=Vcc -> possible that circuit have protection diodes is very high Smiley

Datasheet isn't precise and full informative
« Last Edit: January 30, 2021, 10:56:02 10:56 by dennis78 » Logged
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« Reply #7 on: January 30, 2021, 05:51:34 17:51 »

Don't put more than 5.5V on the APX output pin without a limiting/protection circuit.

I recommend reading the following application notes when using supervisors with PICs:
 - AN820A System Supervisors in ICSP Architectures
 - TB087 Using Voltage Supervisors with PIC Microcontroller Systems which Implement In-Circuit Serial Programming

I usually put two 10kΩ pull-down resistors on the PGD and PGC lines. Don't use pull-ups here, because most ICD programmers have internal 4.7kΩ pull-down resistors.
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h0nk
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« Reply #8 on: January 30, 2021, 10:04:12 22:04 »

O.C. output isn't guarantee that protection diodes don't exist.

Its not O.C., its O.D.: Open Drain.
A true O.C. would have no problems with the programming voltage.

Use a either a supervisor without clamping or an active high output
together with a npn-bjt.

I had no problems with the usual recommended MCLR-connection.
http://www.sonsivri.to/forum/index.php?action=dlattach;topic=69036.0;attach=32197


Best Regards
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metal
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« Reply #9 on: January 31, 2021, 12:11:36 00:11 »

I see, thank you all, circuit is busted, I presume.
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