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'[PIC]: FPP software - pin functions'
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
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
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
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.
http://www.piclist.com hint: To leave the PICList
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