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Altera_Forum
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10 years ago

Cyclone IV configuration - nCONFIG signal and JTAG programming issue

Hi, I have a custom board for EP4CE22E22 Cyclone IV FPGA. I have configured the board for JTAG only mode and using USB Blaster Rev.B for programming. The problem I am facing is that JTAG Scan f...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
10 years ago

Hi,

according to the Cyclone IV handbook, pin 4 of the USB Blaster connector should be tied to VCCA, which s 2.5V in your case, but you connect it to 3.3V. It is not quite clear to me what the USB Blaster does with that signal, so I'm not sure if that is really bad.

However, what bothers me is that you say that nCONFIG goes low. I agree that this pin should be high, since you pull it high, and the Cyclone IV really doesn't seem to have a driver for that pin. Did you check, e.g. using a multimeter that VCCIO is stable? Maybe the DC-DC comes up properly, but then goes into CC or hiccup-mode, which would explain why nCONFIG shows a random timing when going low again.

Another stupid idea: is it possible that you accidentally used the very same pull-up resistor for both nSTATUS and nCONFIG? Or that these are too close together and shorted during soldering? That would also explain, as nSTATUS is driven low by the FPGA immediately after power-up.

Best regards,

GooGooCluster