I want to use the /MCLR pin of a PIC16F18346 as a digital input (asynchronous serial). This signal will come from another PIC so this second PIC will need to be protected against the 12V programming voltage. BUT what does the PICKIT3 do with the /MCLR pin during debugging?

 

I want to use the /MCLR pin of a PIC16F18346 as a digital input (asynchronous serial). This signal will come from another PIC so this second PIC will need to be protected against the 12V programming voltage. BUT what does the PICKIT3 do with the /MCLR pin during debugging?

Don't you need to use LVP for /MCLR to be a input pin?

bit 13 LVP: Low-Voltage Programming Enable bit(1)
1 = ON Low-Voltage Programming is enabled. MCLR/VPP pin function is MCLR. MCLRE
Configuration bit is ignored.
0 = OFF HV on MCLR/VPP must be used for programming

 

Don't you need to use LVP for /MCLR to be a input pin?

When LVP is enabled MCLR is used as a reset. When LVP is disabled MCLR turns into a normal digital input unless the voltage rises enough to trigger programming mode.

"MCLR/VPP pin function is MCLR" is the key here

 

When LVP is enabled MCLR is used as a reset. When LVP is disabled MCLR turns into a normal digital input unless the voltage rises enough to trigger programming mode.

"MCLR/VPP pin function is MCLR" is the key here

I never use the MCLR as port I/O on 8-bit parts so I wasn't sure.

 

I did some digging out of curiosity and found there is not really much information out there on how the debugger actually works. What I could find seems to suggest the MCLR is only used by the debugger as a reset and everything else is done through the normal clock and data lines used for programming.

Since the debugger is enabled by a config bit I'm going to assume it will have to reprogram that bit every time to enable / disable it, but after that there shouldn't be any need for the PICKIT to do anything as far as I can tell with MCLR. Hopefully it releases the pin altogether and switches it's own pin to an input.

Maybe smart to put a resistor between the two PICs along with the diode just in case the PICKIT tries to drive the MCLR one way or the other??? I know it might not be the best for serial speed, but better than replacing puffs of magic smoke.

 

I did some digging out of curiosity and found there is not really much information out there on how the debugger actually works. What I could find seems to suggest the MCLR is only used by the debugger as a reset and everything else is done through the normal clock and data lines used for programming.

Since the debugger is enabled by a config bit I'm going to assume it will have to reprogram that bit every time to enable / disable it, but after that there shouldn't be any need for the PICKIT to do anything as far as I can tell with MCLR. Hopefully it releases the pin altogether and switches it's own pin to an input.

Maybe smart to put a resistor between the two PICs along with the diode just in case the PICKIT tries to drive the MCLR one way or the other??? I know it might not be the best for serial speed, but better than replacing puffs of magic smoke.

Excellent - thank you for your efforts. It sounds definitely worth trying the experiment. Low speed serial would be perfectly functional.

 

Excellent - thank you for your efforts. It sounds definitely worth trying the experiment. Low speed serial would be perfectly functional.

No problem. I have always been curious about the debugger, but never bothered to look in to it. Unfortunately I have a bad habit of connecting PicKits wrong and had to come up with a different way of doing things before I burned up another one.