Hi,

I'm looking for help understanding the functions available with David
Tait's FPP software, for use with a homebrew programmer.

My aim is to ICP a PIC and leave the programmer attached while testing,
virtually regardless of the usage of RB6/RB7 in the real circuit.

For this I will need to be able to tri-state the programmer outputs to
RB6 & RB7 for normal PIC running.  RB7 also needs to go tri-state during
program verify phase.

In addition I need to be able to raise MCLR pin to Vpp, or allow it to
'float' to Vdd in the real circuit, and AFAICT, I also need to be able to
ground MCLR to reset the PIC (or at least FPP needs to, but I could be
wrong).

The readme for FPP says:

        OUT  -- data from the PC to the PIC (usually RB7)
        CLK  -- clock from the PC to the PIC (usually RB6)
        VDD  -- turn on the PIC +5V supply (not always needed)
        MCLR  -- control the PIC /MCLR pin
        PGM  -- used (with MCLR) to establish programming mode
        READ -- high when PIC must be read
        IN   -- data from the PIC (RB7 again) to the PC

CLK, IN & OUT are straight forward enough.

MCLR is the next easiest - obviously it is intended to either pull MCLR
pin low, or allow it to go high (even to 12V if this is sole control of
Vpp).

The Stop/Run button will toggle MCLR, but you wouldn't want to run with
12V on the MCLR pin, so I guess this is where PGM comes in.  But how
exactly?  Does it stay on throughout program & verify?

VDD seems simple enough, but again is it stable throughout, or switching
off between read and verify phases?

READ: now I am really hoping I can use this to tri-state the connection
to RB7.  Otherwise what could it be for?

It would help a lot to see the order of the above signals through a
whole program, verify & reset sequence - then I could see how best to
use them for my programmer.

I already have a working circuit using just CLK, IN, OUT & MCLR, with
manually switched 12V supply.  It's not really good enough as a portable
ICP though because of the restrictions on the use of RB6/RB7 in the real
circuit.

I.e. without tri-stating, the programmer needs to have source impedance
to allow the real circuit to run with it still connected, but then the
real circuit loads can interfere with programming.

Can I do this with FPP?  It's the most flexible programmer software I
have found yet.

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