AVR-Chat

Please help to confirm this understanding of sharing the JTAG pins.  I know it works with ISP, but JTAG seems to be less clear...
 
I want to use the 4 JTAG pins as output pins in the normal mode operation.
 
However, for debugging, I also want to use these 4 JTAG pins to run ICE.  
 
As I read the Atmel documentation, it seems that works fine under 2 assumptions:
 
A. The output for these 4 pins is isolated somewhat (dip switch or series resistor between MCU and the other load - but the JTAG connection is direct with no resistive isolation)

B. When running ICE via JTAG, these 4 pins will NOT be available as output pins - as their function at that time will be dedicated exclusively to JTAG.
 
The Atmel document shows only a mention of "LOAD" via a set of resistors.  And no other mention.  So I am unsure if this is correct.

Appreciate any comments the group may like to share.
 
Thanks/jeff

At 10:16 AM 16/10/2009, you wrote:
>The Atmel document shows only a mention of "LOAD" via a set of resistors.
>And no other mention.  So I am unsure if this is correct.

Your other 2 assumptions are correct. Using the JTAG pins while
connected to something (ie LEDs or switches for run mode) needs
at least 1K resistors in series with each leg. (your "LOAD")

Regards

John Samperi

********************************************************
Ampertronics Pty. Ltd.
11 Brokenwood Place Baulkham Hills, NSW 2153 AUSTRALIA
Tel. (02) 9674-6495       Fax (02) 9674-8745
Website  http://www.ampertronics.com.au
*Electronic Design * Custom Products * Contract Assembly
********************************************************

Thank you very much John.  That is what I needed to know.

Regards, Jeff

From: John Samperi 
Sent: Thursday, October 15, 2009 10:18 PM
To: AVR-Chat@yahoogroups.com 
Subject: Re: [AVR-Chat] Sharing JTAG test pins as I/O


  At 10:16 AM 16/10/2009, you wrote:
>The Atmel document shows only a mention of "LOAD" via a set of resistors.
>And no other mention. So I am unsure if this is correct.

Your other 2 assumptions are correct. Using the JTAG pins while
connected to something (ie LEDs or switches for run mode) needs
at least 1K resistors in series with each leg. (your "LOAD")

Regards

John Samperi

********************************************************
Ampertronics Pty. Ltd.
11 Brokenwood Place Baulkham Hills, NSW 2153 AUSTRALIA
Tel. (02) 9674-6495 Fax (02) 9674-8745
Website http://www.ampertronics.com.au
*Electronic Design * Custom Products * Contract Assembly
********************************************************





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