Guru
Joined: 06/06/2011
Location: AustraliaPosts: 3368
| Posted: 11:31pm 31 May 2017 |
There is an internal weak pullup applied on COM3 when it is opened and that is probably the cause. You can disable this by installing the ChangePin CSub (included in the Micromite zip) and using it like this: ChangePin 26, 15
You are right to be anxious about using only the 1K resistor. It was assumed that protection diodes on the input (most micros have them) would clamp the voltage to Vdd but with further investigation I have found that on the PIC32 there are no protective diodes and no clamping. The best way to go would be to use an external general purpose diode (eg, 1N4148) from pin 26 to Vdd to clamp the input.
An alternative would be to use a voltage divider as you did and turn off the pullup.
Geoff
Geoff Graham - http://geoffg.net