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How does a JDM2 circuit work?

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Jul 12, 2009
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jdm2 programmer

I try and make some PicKit2 clone like Junebug but for that I need program PIC somehow.

I find JDM2 circuit that need no preprogram PIC so I can program PIC from start.

I see small JDM2 circuit : **broken link removed** or **broken link removed**

But circuit very simple but confusing.

No one write what circuit do or how it program PIC.

How it works?

jdm 2


Can understand you looking back at the JDM type programmers again.

Even built correctly they may not work on you PC as apparently the way serial ports are built on the more modern motherboards means that the JDMs do not always work - think its something to do with current avaialable from certain pins.

The P16Pro type Parallel port programmers will work well enough to progam some some of the 16F and 18F chips including the 18F2550 needed for a USB programmer.
I've attached a pdf of a little board I made up.

Still recommend you go for the Pickit2 , ready built or a diy version - it really is the best thing since sliced bread and by far the best value.

I understand that a diy version needs the 2550 chip to be programmed up first, and assume there is no one only you know locally who can help there - however would suggest if you name your country some other 'local' member would be happy if you sent them a chip and they would program it up for free.

Hi wp100,

you are always help :)

I have search for may programmers and see all design.

I see parallel, serial and USB but no design so simple and effective as JDM!

It is magic to me!

I have made the parallel programmer you give and now I program 2550 to blink lights!

Soon JuneBug I make :)

But I want to know the magic of JDM - please I need explanation.

Added after 56 minutes:

By the way wp100 - what firmware from PicKit2 zip file from Micsochip site to use as firmware for JunebUg pray tell?


JDM has detailed explanation of his basic design:


It is a good starting point.
jdm2 diy


Good the hear that you have got something working and you can program away

But I want to know the magic of JDM - please I need explanation.
Think that link from Blue Snake is the fullest description I have seen.

Be aware that the programmer hardware is only the last step of a complex programming method, the software is equally important as is an understanding of the way the chips memory is actually programmed.
If it was that easy then why cannot the jdm or the Pro16 programmmers program all the microchips ?

what firmware from PicKit2 zip file from Micsochip site to use as firmware for JunebUg pray tell?

The software to program up the 2550 chip for the PK2 is from microchips file Pickit2 Firmware 2.32.ZIP - file PK2V023200.HEX

It is important that you run all the programs from the same generation - that is Mplab 8.30+ , Pickit2 Programmer Application 2.61 and Pk2 firmware 2.32.

How the Junebug uses its own code and the Microchip code ? you need Bill, the designer / owner of Blueroom Electronics to answer you that one.
usb jdm2

Ok, question:

1. If I put 13V on MCLR then PIC will be programmable?

2. In this state I put PGD, PGC so it program?

3. If I not need verification then no need to supply 5v to Vss at all?

jdm2 circuit


Yes, its just the four lines to program most chips, but its how those lines are controlled that is very important.

Mclre and VDD must come on in certain ways and the speed, rise time, of these 2 rails is also important.

If you want to look into the heavy subject of programming chips go to Microchips site and seach with this phrase ' Programming Specification icsp '

You will be able to see plenty of info, but think you will be dissapointed because as you will see each type of chips has there own strict method of programing its memory.

There is no single universal method in that sense - hence why the 'hardware' of programmers are not so important, its there ability to be controlled by software that is.

With the Microchip range of Pic chips for the average diy enthusiast the Pickit2 is the best unit as it from microchip and its software is regularly maintained and updated with new devices and occasionally new functions like the Logic Analizer.
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