Just to update everyone. It seems the SERR errors are due to noise on the PCB or in the power supply. Changing the logic options for all outputs to SLOW SLEW RATE reduced the chance of an error. Maybe Altera Cyclone devices need a very good PCB and large amounts of decoupling for the power. I will modify the PCB layout and make some more to see if I can improve the PCB so I no longer get errors. Thanks to all who replied. Dave Warren dave@luscher.co.uk

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