My current SigmaDSP project uses four GPIO pins - MP2,3,8 and 9 - as digital inputs. Their read values are scaled and used to control various switches and multiplexers.
MP2,3 and 9 work perfectly. However, MP8 always reads as low. I have monitored it using the read/write window and there is no change when voltage is applied.
If I link MP8 to MP11 on the PCB and alter SigmaStudio to read MP11 instead, it works perfectly.
My input pins are pulled down by resistors, but I can see a small residual voltage from the internal pullups on all of them, so MP8 must be correctly configured as an input.
My initial thought was that the DSP must have been damaged during prototyping, or something similar, but I have built three prototypes and they all behave in an identical way.
Can anyone replicate this behaviour? Am I doing something silly (I never rule that out)? If it IS an "unintended feature", are any other pins similarly affected? It isn't actually a problem on this project (there are many other GPIO pins I can use), but I am worried in advance about my next project (quad micro-assisted ADAU1701s) where I need all the GPIO pins available.
Thanks and kind regards,