Spartn 3 configuration failure

Hello,

I am a newbie to the group and FPGAs in general. We have a board with XC3S1500 FPGA on it. We use the master serial mode to configure the FPGA using a platform flash (PROM) with the FPGA providing the CCLK (confg rate -50). For debug reasons we also have the confg. signals going to a POD header.

We see that sometimes when we probe the CCLK on the POD header the FPGA fails to configure. On the scope , we could see the sequence of INIT going high, CCLK going active (clocking), DONE being low and after some time, the INIT goes high, the CCLK stops clocking but the DONE pin does not go high. We have 330 ohm pull-up on DONE pin.

If i remove the probe from the CCLK pin on the POD header the board starts-up with successful configuration.

I was wondering if anybody in the group has seen such behaviour before or may be the experts in the group could guide me on the possible issues involved.

Also, sometimes I have also seen that as the INIT goes low, CCLK goes high but does not begin to clock . In this case, a configuration failure is obvious. So, is this a problem with the chip not being consistent?

Thanks a lot in advance

Regards Nithin

Reply to
nithin.pal
Loading thread data ...

Ah, i'd be careful probing the configuration signals while the device is programming-Make sure you have the scope set up so that the impedance of the Probe is not going to unduly effect the quality of the signals on the board.

From what you say it sounds like the probe termination is interfering with the signals you're scoping. it can happen if you have slow probes, i.e. old stuff, or if you have the termination of the scope set to something untoward, (50-Ohms would probably kill your config) anyways, even if it looks great on the scope, you might be making some standing waves later down the line.

HTH Ben

Reply to
Benjamin Todd

Hi pls see the errata of that particular device. we had a similar problem, which was due to the power supply sequencing,1.2 V should not be the last one to come up, this is applicable only for some particular batch of spartan-3 chips from their new fab.

Reply to
bijoy

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.