JDM ICSP programming ok, but causing reset of circuit

[anthonybradley]

Hi,

I have built a JDM programmer, and it programs 16F876 ok, either in or out of my project circuit, but the project circuit (just PIC running an LCD) will not run with the JDM ICSP connected.

When I have finished programming and power up the circuit whislt the JDM ICSP is still connected, MCLR seems to get pulled down to 0v which obviously keeps the PIC reset.

I have a 10k resistors between MCLR and Vdd, and a diode to the power rail as documented on the JDM site **broken link removed**

The only way I can run my project circuit is if I either disconnect the ISCP lead, or unplug the JDM programmer from the serial port so its not powered.

I have tried closing ICprog just incase that was making the JDM do something wierd after programing, but same problem still

Anyone else seen this or have any idea why the JDM is pulling MCLR to 0v?

Am I being really silly, you are supposed to be able to leave the ICSP connected to the circuit when not programming arn't you? :?:

This is driving me mad!

many thanks,

anthony

 

[Nigel Goodwin]

Am I being really silly, you are supposed to be able to leave the ICSP connected to the circuit when not programming arn't you? :?:

I think you perhaps are?, the JDM isn't designed to be an ICSP, a circuit designed to do so 'could' allow the PIC to run with the programmer connected. But the crude 'least number of parts possible' JDM certainly can't do it.

The reason is quite simple, a programmer requires MCLR to be either ground or +13V, for the PIC to run requires +5V on MCLR (a level the programmer can't provide).

I have, in the past, written custom versions of WinPicProg designed to do just that, with extra hardware - and extra buttons, 'Run' and 'Reset' on WinPicProg's main screen.

 

[anthonybradley]

ah...ok....ooooppps

Ah ok, that will teach me to chase ideas without thinking them thru


Guess I'll just put a 'program / run' switch in the ICSP cable to disconnect MCLR and Vdd from the programmer to run the code, and connect them back again to program it.

Many thanks!!!

Anthony