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You want to BUILD your own from existing schematics, or complete make your own new schematics and build it? If the second, why, since there are tons out there. Search for THVP or TLVP by Byron Jeff for the simplest programmer I have found.
Do you mean hardware programmer? Or develop both the software and the hardware?
I have spent many hours (days) in the past searching in the net to find a simple programmer. With pic16pro40 I was able to program my 16f628a as well as 18f252. However the most simple solution I have found is a programmer using only resistors, driven by the ICProg software programmer: http://home.t-online.de/home/520054661375/stolz.de.be/lvpc/index.html (This is the same site hosting the simple ICD2 circuit). With this "resistor only" programmer and ICProg, I easily programmed 16f628a, but I had no success in the 18f series.
However this simple programmer gave me the idea to make my own software programmer - you have just to control 3 or 4 pins of the micro anyway, why should this be difficult??.
What would be the point in this?? ICprog seems to me that does not support newer 18f micros such as 18f2620 and 18f2550(usb) (from which I have samples) - at least there are not in the drop down list.
So I downloaded the Flash programming specification from microchip, and studied it and I think if someone knows programming could be able to build one software programmer...
I dont have the time to completely build a soft programmer now, because I am in the middle of exams, but what I have done till now follows:
I decided to use the parallel port for the interface - my parallel port logic high is 5 volt , newer may not be the same... I also didnt want to bother with high voltage (13volts) so I went for Low voltage programming. A simple trick that I used and helped me a lot, had to do with the PGD signal which is either input or output (during read): I used the parallel port in SPP mode which is bidirectional (toggling a single bit in control register -0x37a- you can toggle the Di pins of LPT between input and output mode). The other 3 pins that were always outputs (from the LPT view) I decided to be control pins.So I used:
1. a wire to connect LPT ground and pic micro ground
2. a resistor (330 ohms) to connect LPT.pin2 (D0) to PGD pin of pic micro
3. a resistor (330 ohms) to connect LPT.pin1 (I dont rem now) to PGC pin of pic micro
4. a resistor (330 ohms) to connect LPT.pin17 (I dont rem now) to PGM pin of pic micro
5. a resistor (330 ohms) to connect LPT.pin14 (I dont rem now) to MCLR pin of pic micro
I then wrote a simple program just to read the Device ID (at memory loc 0x3FFFFF:0x3FFFFE for 18f series). I had a loop reading constantly the device ID and printing it on screen. For the 16f628a this was successful from the first time. For 18f i found that it needed a small capacitor between PGC and Vdd. I have read the device ID and configuration registers for 18f1320, 18f2620, 18f2550 with 100% repeatability...Maybe someday could become a full programmer..
If you are interested you could begin downloding the flash programming spesification for the device you want and try to make your own programmer. Good Luck!
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