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AVR JTAG ICE - Target System Design

This page presents some advice regarding adding a JTAG connector to your AVR-based system during design.  The Atmel JTAG ICE User's Guide is the definitive source of information on this subject and nothing here should be taken to contradict or supercede it.

The JTAG Header

The picture at right shows the layout of a JTAG ICE connector on a target system.  Pin 1 is located near the edge of the board, which is at the top of the picture.  This means that the ECROS Technology AVR ICE-Cube can be plugged directly onto the header and will hang over the edge of the board, not blocking access to any components on the board.  If you do not want the connector to be at the board edge or you need it mounted the other way round, with pin 1 on the inside, there are two choices.  You can make sure that there is nothing under the ICE-Cube outline that is tall or to which you need access and still plug it directly onto the header.  Alternatively, you can plug the ICE-Cube into its cable adapter and run a ribbon cable to your target system.


Connect the header pins as follows:

Pin # Name Direction Connect to:
1 TCK Adapter to target TCK pin of target MCU
2 GND - Target System Ground
3 TDO Target to adapter TDO pin of target MCU
4 VTref Target to adapter Target System VCC †
5 TMS Adapter to target TMS pin of target MCU
6 nSRST Bidirectional RESET pin of target MCU
7 Vsupply Target to adapter Target System Power Source ‡
8 nTRST Adapter to target not used, do not connect
9 TDI Adapter to target TDI pin of target MCU
10 GND - Target System Ground

† Current is not drawn from pin 4, VTref, to power a properly designed JTAG ICE interface device.  This pin is only used to sense the target power voltage.  The maximum current draw at this pin (at 5.5V target supply voltage) is less than 40 ľA for the ECROS Technology AVR ICE-Cube.

‡ Do not connect pin 7, Vsupply, if you don't want the JTAG ICE interface to be powered from the target system or vice versa.  Nevertheless, connect pin 4, VTref, so that the JTAG ICE can monitor the target system supply voltage.  The AVR ICE-Cube draws 13 mA from the target system at 3.3 volts and 22 mA at 5 volts.

Click this button to go back to the ECROS Technology AVR ICE-Cube introduction.