Hi David,

> Here is a circuit I devised recently for a simple RS232 based parallel
> interface that had only three outputs available.
THREE outputs with RS232???
I only know of RTS and DTR. Or do you abuse the TxD line like the Erik-
Hermann-ultracheap-RS232-programmer?


> Note for this circuit to work the MCLR line is tied to the system VDD via
> a diode and 1k resistor on the target board
That is another point to discuss. The data book says, MCLR must be at least
0.85*Vdd, that is 3,06V at Vdd=3,6V, the difference is 0,54V.
Microchip writes that the MCLR pullup resistor should be not greater than
1k so that the voltage drop at MCLR input with respect to Vdd is smaller than
0,2V (!). With your circuit it seems to be hard to meet this specification:
a 1k : 10k voltage divider together with a diode? Just calculate yourself.
PICs are probably less critical as my (Microchip's?) assumptions are, and
work without problems...


Some notes about your famous 'Basic PIC 16C84 programmer':
I think it is easy to expand and optimize your programmer's design so that it
meets 'my private' specifications by using all the unused drivers of
both ICs. Only one more line of the PC's parallel port would be needed and
therefore the software has to be adapted (which is the only disadvantage).
Interested?


Cheers,
Siegfried