Cheers All,
The primary reason for sourcing the LED's and 'shorting' the one on the RA4 is that all the LEDS (over 200 of them) are already installed and wired, as these units are replacing the existing driver circuits which was pure TTL logic which were very old and there were no replacement parts available.
My 'Brief' was to come up with something to replace the driver circuits, and have ample replacement spare part capability, hence I chose the PIC16F628A as this was my first venture into PICS, but have broken the cardinal rule of design, and did'nt read the data sheet properly ...
However, the PCB I designed has multiple functions and can be configured for either 12 inputs / 12 outputs or 6 of each, hence a 12 channel combo board, with 'on board' pull up resistor SIL networks and driver resistor positions, reset circuits and Tx/Rx comms, which fortunately allowed the function of the RA4 circuit to be implemented 'as though it was designed that way' ... so there are no links, mods to the board etc.
Pommie,
I did try your suggestion, but did'nt expect it to work, which it did'nt.
I think the reason is that when the system is first powered, the RA4 output is high impedence, and hence the LED (and its resistor/anode junction) are 'HIGH' so the LED is ON, there is an inherent delay in the PIC starting up (even without the programmed 72ms start up delay).
Hence you do get thes short 'ON' time until the PIC initialises.
As Nigel indicated, I have been doing this for years with Micros especialy using transistors/switches to discharge capacitors on Micro Reset circuits before we had WDT chips available.
Thanks for all your posts ....
Roy