Help understanding jdm

[throbscottle]

I keep going back to study the original jdm programmer design because it's so clever. But there are a couple of questions I have. I'm building my own usb variant (with boost converter to get vpp) and want to maximise the chances of it working! I'm using a cp2101 usb to uart bridge dongle. I'll post diagram when I finally get to test it.

I refer to the diagrams here https://www.electro-tech-online.com/threads/jdm-for-16f84a-20i-p-and-16f874-20i-p.3005/ because jdm.homepage.dk seems to have disappeared.

I know txd is used to generate the power, but I've seen references to reading back from the chip via the programmer. So is txd controlled by the software to turn off in order to read (and the 5v then just comes from caps?)?

In jdm3 an extra output is added to dsr. What is this for? Does it tell the software that the programmer is powered up?

I've looked at quite a lot of variants, with various resistor values between cts and dtr, or just a short. Where present, what is this resistor for?

I've connected cts straight to dtr since it looks like the resistor is related to rs232 voltage levels. Same goes for Q2.

 

[blueroomelectronics]

JDM is a rubbish programmer. Try building a PICkit2 Lite instead, catch is you'll need to load the bootloader on the 18F2550

 

[mvs sarma]

Suggestion of buleroomelectronics is more apt as you might use the programmer for a long time.
In these modern days it would become difficult to find COM port on laptops and even many desktops are not providing COM port of late.

If still you prefer JDM with power drawn from usb socket, there is one variant of COM port based Programmer with external powering that would not need usb power management. even the regular PICKIT2 is not getting enough power at times from the usb socket. The experts recommend externally powering usb adapter to overcome the issue.

All said
a regular version of PICKIT2 would be better. once pickit version is agreed upon, the additional load not not much to incorporate the Vdd adj .

 

[throbscottle]

I believed jdm's shortcomings were because it draws power from the rs232? Otherwise it's just icsp, a widely used standard, but with high voltage, isn't it?

Anyway I'll just have to see how it goes. I haven't tested what current mine draws yet but it should be well within usb capability.

Cost-wise, I built this thing from scrap, bridge was under £1, zif socket was under £1, already had the veroboard, everything else was free.

 

[Nigel Goodwin]

I believed jdm's shortcomings were because it draws power from the rs232?

Mainly because it was using the handshake lines from the serial port in a non-standard manner, and relied on the port voltages exceeding the RS232 specifications.

So they worked with some ports, and not with others, and may work one day but not the next.

Otherwise it's just icsp, a widely used standard, but with high voltage, isn't it?

Anyway I'll just have to see how it goes. I haven't tested what current mine draws yet but it should be well within usb capability.

How does that help you?, a USB port isn't an RS232 port, you don't have individual access to handshake lines etc, or even the port directly.

As far as I'm aware, the only way to make a USB programmer is to have a processor on board (that does the programming) with the USB simply transferring the data.

As the author of the worlds first Windows PIC programmer software I would seriously suggest using a PICKit or clone.

 

[throbscottle]

Ok I'll consider myself well and truly informed! Thanks Nigel

 

[mvs sarma]

As the author of the worlds first Windows PIC programmer software I would seriously suggest using a PICKit or clone.

Nice Nigel
I didn't notice this earlier. I remember your contributions on h/w and .asm
tutorials that really help any new entrant , and guide even seniors for concepts.

 

[Nigel Goodwin]

As the author of the worlds first Windows PIC programmer software I would seriously suggest using a PICKit or clone.

Nice Nigel
I didn't notice this earlier. I remember your contributions on h/w and .asm
tutorials that really help any new entrant , and guide even seniors for concepts.

It's my "claim to fame"

I decided to write Windows PIC programming software for three reasons:

1) To teach myself Windows programming with Delphi.

2) No one had done it before.

3) I already had my Turbo Pascal DOS programming code, with in-built disassembler (another first).

 

[mvs sarma]

It is comforting and a matter of pride, Nigel. Wish you good health and many more tech supports to deserving members.

 

[throbscottle]

Actually I just read the datasheet for the bridge chip, it claims to support hardware flow control - doesn't this make it similar enough to a real port?

 

[Nigel Goodwin]

Actually I just read the datasheet for the bridge chip, it claims to support hardware flow control - doesn't this make it similar enough to a real port?

No, JDM's barely work anyway - and their unreliability was the reason WinPicProg only supported parallel port programmers, even though it would have been a trivial task to add a serial 'port' option.

I offered free support for my free software, adding the JDM would have been just asking for trouble.

PIC programming is all about toggling I/O pins, with fairly accurate FAST timings, USB doesn't provide that level of control or accuracy. USB programmers (like the PICKit series) use an on-board processor to do all that, and simply transfer data (via the actual USB port) to the processor, which does everything else.

 

[throbscottle]

Ahhh. Well, I've read and read and read about this, and nowhere have I found the pure gold information you just given me. Everyone says this and that, but without the reasons. Heartfelt thanks for the reasons

I'll give it a go anyway since it's built now (once I've got Arch to recognise the serial port - fell over at first step, duh), if it doesn't work, well I can't afford a real pickit, but **broken link removed** clones seem cheap enough.

 

[mvs sarma]

you can make one as DIY
only a single sided pcb to be made locally and master pic18F2550 to be got firmware loaded once. if needed a PCB can be sent by me, but international courier becomes costly.
anyway check for possibility of pcb etching and i can support you for the artwork etc. The artwork is a full complement of microchip's PICKI2

 

[throbscottle]

Thanks Sarma - but as blueroomelectronics points out, I need to program a pic to make a pic programmer. Suppose I could get someone to do it for me. If I do this I'd certainly appreciate your artwork, however I'm ok to do my own etching

 

[mvs sarma]

i shall soon post the set of diagrams on pdf. Artwork done by eagle and pdf created.

I shall explore the cost of sending, if possible send it to make life easy.

 

[mvs sarma]

Hope these files are sufficient to make your DIY board and populate it. All the best

few notes:
I had problems with pin type mosfets BS170 and BS250. i now use NDS356 for p-mosfet (BS250) and and si2302 for n-mosfet( BS170). i mount them on solder side itself with due orientation. These smd mosfets are easy to mount for an young man like you. they can be had from either RS components or Farnell.

 

[throbscottle]

Tried it on the PC. Had to fiddle a bit, just tried testing with blank check and read since my test program is on the lappy. Looks okay.

 

[mvs sarma]

i was suggesting "winpic800" driver from www.winpic800.com with JDM configured under hardware

 

[throbscottle]

Hi Sarma
I gave it a try as you suggested, but the version I'm using is the only one that controls the port properly. I also tried picpgm, which works sometimes.

I have just been testing the voltages on the dongle whilst sending data to the port. rts and dts only go to 3v, nothing seen at txd when sending a text using sscom32e, even though it shows up on serialmon. So I need buffers. Don't know what's going on with txd - good job I'm not using it!

 

[mvs sarma]

this programmer from DL4YHF worked for many of us under WinXP. What is the pc (motherboard)/ latop and the OS you use ?