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Altera_Forum
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14 years ago

Intermittent JTAG with MaxV Device

I am fairly new into JTAG programming of devices. I have a new design with a MaxV CPLD. The first run of prototypes we had forgot the pullup/down resistors in the JTAG chain. After adding those...
Altera_Forum's avatar
Altera_Forum
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14 years ago

Thanks for the replies. Issue was finally solved.

1. VCCINT was running on 3.3V instead of 1.8V (my mistake, but it was not causing the JTAG issue, strangely enough the CPLD appeared to run normally @ VCCINT=3.3V)

2. A logic level RS232 device was connected. The Tx of this device was running at +5V levels. There is a filter in this line that weakens this signal. Disconnecting this device brought JTAG performance back to normal. Funny that a relatively weak TTL level signal can have this effect and that it took me so long to figure this relationship out.

JW