I'm trying to make a programmer for the 8051 microcontroller IC's, specifically the AT89C2051. I saw a circuit online (the blowit programmer) in which the unused GPIO pins are left floating.
When the 8051 is in normal execution mode, the outputs are always high-impedance or grounded, and applying external ground never hurts the IC, but applying external VCC causes the IC to not operate correctly if I set a logic low on the same GPIO pin in software.
I checked the datasheet and it does not mention anything about the state of the pins that are not used when programming the IC.
I'm curious. For this IC or any other 8051 based IC, is it a problem if I ground all unused GPIO pins during programming?
I also think if I can do that, then a side benefit would be less noise, but then again I'm not sure if that benefit applies because each GPIO pin has an internal pull-up resistor.