I use EP3C16Q240C8N FPGA on our custom board. I have been working on the same board more than one year. Last week one of my board gave an error and I could not program this board anymore. I searched the problem on HW and found that TDI programming pin on JTAG (Pin Number 26, EP3C16Q240C8N) seems to be pulled down. Because when I measure the resistance of this pin between ground, it gives 3.6 ohm like shorted circuit. I measure the resistance of a normal board the resistance between TDI and GND is around 11 KOhm. This make me think of if my FPGA was broken down.
It is strange that when I energized the board it reads the EEPROM (EPCS4) and working properly but I can not program the FPGA again.
Does any one know the problem?
Since you are able to make it working properly with EPCS4, your FPGA still okay. However, I suspect your JTAG connection is not working properly.
If I got extra information regarding to this issue, I'll get back to you.
In the meantime, can you check all of your JTAG connection pins (TCLK, TMS, TDI,TDO)? Please follow the pin guideline below:
We checked the JTAG connections again. Everything seems to be ok. Actually I have four of the same boards all of them working properly and three of them can be programmed but one of them can not. The board that can not be programmed was also programming during the past 12 months. But something happened, I dont know why, and then We have not been able to program it again. Do you have an idea about the issue? Or what information else we need to give you in order to you understand the issue?
We will be appreciated of your help,