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Pickit2 tri-state

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2007-2009 » Archive through 28 December, 2008 » Pickit2 tri-state « Previous Next »

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mikeb
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Username: mikeb

Post Number: 57
Registered: 02-2008

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Posted on Thursday, 27 November, 2008 - 03:55 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I got my pickit2 a week or so back - nice one EPE.

I need to use rb6 and rb7 whilst in development and I had hoped that these pins would be tri-stated by the programmer when not needed.

Unless I go to Low Voltage programming, it seems to be impossible to instruct the programmer to tristate the program lines.

The Microchip advice is to use resistors to isolate the programmer, but I cannot see how that will help.

Is this still an omission from Microchip or have I missed something here?

rgds

mb
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epithumia
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Username: epithumia

Post Number: 596
Registered: 06-2006

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Posted on Thursday, 27 November, 2008 - 04:10 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I don't use pickit2 but...

I usually put 220 ohm resistors between the PIC and the programmer. That allows the PIC to drive RB6/7 even when the programmer is connected, or bidirectional data to a device such as an LCD display. It allows my circuit to override the programmer's outputs.

Of course, it wouldn't work with a high impedance circuit driving the PIC.

Epi
If you need me, Neil and me will be hanging out with the Dream King. - Tori Amos
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mikeb
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Username: mikeb

Post Number: 58
Registered: 02-2008

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Posted on Friday, 28 November, 2008 - 12:34 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks for comments epi.

Yes, I have a keyboard hanging off the port, so its difficult to 'share' the pins.

It seems amazing that after all this time, a Microchip product still does not tri-state the progam lines.

I am now building a small isolation circuit, based around those analogue switches (4069 is it?), enabled by MCLR.

rgds
mb
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mikeb
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Username: mikeb

Post Number: 60
Registered: 02-2008

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Posted on Sunday, 30 November, 2008 - 08:58 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

If anyone is interested I have built the isolator using a 4016 quad switch. I may docmnet and send to EPE.

rgds
mb

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