Hello, I just wanted to confirm proper hardware configuration for ADuC845 unused digital I/O and A/D pins. I am planning on taking these pins to ground, but wanted to verify this was the proper thing to do.
I would connect the open ADC inputs direct to AGND - not connected pins are always subject to EMI (Electromagnetic Interference) issues.
The digital IO pins are comparable to the original 8051 design including the internal pullup resistor. Because of this pullup connecting the pins to ground will consume unnecessary current. On the other hand the pullup provides a defined high level on the pin. The original recomendation for noisy environments was to connect unused pins to the supply via an additional external pullup resistor. A problem with tieing pins directly high or low is that if the IOs are accidentally configured as outputs you could get large output currents that are potentially damaging over time.
On the unused analog pins it should be fine to tie them to ground but it would also be acceptable to leave them unconnected.
Hi EckartH, thank you very much for your help and information regarding proper configuaration of unused pins on the ADuC845 micro.
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