Honored Contributor
Honored ContributorI understand, that you´are generally searching for a reliable JTAG solution, had no bad experience with your own designs yet. This is my situation, mainly.
I can't answer your questions exactly. Fortunately, I'm not in a duty to do, but I would like to know myself. I want to perform some comparative measurements with different JTAG adapters, I have to collect them from customers or friends. I already checked the Altera Rev. B Blaster. I previously stated, it produces overshoot due to it's special level converter. I fear, the explanation is too simple. Clearly, the level converter had been changed with Rev. C and Terasic Blaster, so one could easily suspect a problem related to this design detail. But Rev. B doesn't show severe overshoots or even double clocking with a lot of boards. There are problems with some designs only. I checked with EP2C35 Nios II Board and it's fully O. K., functionally and also looking at the signal quality. I believe, the special Rev. B problem is in combining the MAX3378 level translator with a unsual low impedance (around 20 ohms) embedded stripline flex PCB as a cable. Possible impedance matching problems are shifted behind the JTAG board connector this way. Some users replaced the flex PCB with an IDC cable for different reasons (more robust and flexible, not breaking as easily, needing a longer cable). This totally changes the impedance matching, cause an IDC cable outer conductor has about 150 ohms impedance to an adjacent ground wire, causing serious overshoots with a longer cable. When I have time to finish the comparative measurements, I'll compile the results and present them at the forum.
