AVR JTAG USB - Connection Glitch?

Development Boards MicroMod
1

I am using the AVR JTAG USB for the first time, and on a new PCB design (ATmega32L). When I power my circuit with the JTAG cable connected, the LED on the AVR JTAG USB comes on as expected. However, when I start AVR Studio and try to connect to the AVR JTAG USB, the LED immediately goes off, and the connection fails!

This is a 3.3v circuit, and I can see the 3.3v on pin 7 of the JTAG connector, and it is still there uninterrupted when the LED goes off. After this occurs, if I depower my circuit and power it up again, the LED comes on again.

Help! What bone-headed thing am I doing wrong or mis-assuming? Thanks for any suggestions…

  • Michael
2

Apparently, on the JTAG connector, you must have both pin 7 (VCC) and pin 4 (VREF) tied to V+ to successfully use the AVR JTAG USB. It derives power from pin 7, but AVRStudio requires that at least 1.7v be applied to VREF or it assumes the target device is not powered up.

This is a very simple requirement, but I didn’t see it clearly stated anywhere a beginner like myself might see it.

  • Michael