DIY Comms Link?

This special section for all the COMMS LINK and communications issues
okto
Posts: 61
Joined: Sun Apr 23, 2023 5:14 am

DIY Comms Link?

Post by okto »

Has anyone made their own? Paying $70+transatlantic shipping for the one on eBay doesn't sit with me for what's essentially a tiny PROM, a level shifter, and a buffer.

Is there a PCB design available?
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Martin
Global Admin
Posts: 250
Joined: Mon Jan 02, 2023 5:18 pm

DIY Comms Link - Technical Information

Post by Martin »

Dear Okto

Yes members have made their own Comms Links and others here will contribute to the hardware design..

In the mean time check out the Comms Link page (here).
And there is a Schematic in the Technical Reference Manual page (here).

Sincerely
Martin

PS Yves who is hosting this Forum is a Canadian member so shipping might be simpler for some items.
amenjet
Posts: 237
Joined: Tue Jan 03, 2023 7:54 pm

Re: DIY Comms Link?

Post by amenjet »

okto wrote: Tue Apr 25, 2023 11:24 pm Has anyone made their own? Paying $70+transatlantic shipping for the one on eBay doesn't sit with me for what's essentially a tiny PROM, a level shifter, and a buffer.

Is there a PCB design available?
The comms link schematic is on the web, yes. I'm not aware of any re-creations of it, though. A lot of PCs these days don't have a serial port any more so people find a USB adapter more useful. There is a schematic for that on the web as well. it's quite a challenging circuit and build, though, so it might be better to take advantage of the very nice design feature of the original comms link PCB that makes it a general serial interface design. The same PCb was used for the comms link, barcode reader and anything else that used a serial data link. See here:

https://www.jaapsch.net/psion/galdev1.htm#comms

for pictures of the different versions of the commsn PCB and here:

https://www.jaapsch.net/psion/topslot.htm

for the different wiring used for various different devices. The comms link PCB is called the 'Top Slot Interface' in that document.

What are you trying to do? i might have some PCBS and/or designs floating about that you can use.
Shipping these days is a real problem, prices are higher and some couriers seem incapable of not losing packages. The one thing that has been reliable for me, though, is shipments of PCBs from the Chinese manufacturer i use. They've got a bit more expensive but are now, I think a little bit faster. And so far 100% record of actually delivering the package. No losses at all.


Andrew
Bumblemittens
Posts: 32
Joined: Tue Apr 04, 2023 9:11 am

Re: DIY Comms Link?

Post by Bumblemittens »

Hey folks, so i built the comms link pcb, no magic smoke was released so that's a plus, however it is not seen by the organiser not even reporting a bad pak, i burnt the comms42.opk to the eprom as is, I understand that because of the design the data on eprom is scrambled, I'm not sure which comms image i should be using

As an after thought I'm burning the EPROM with EPROM programmer not datapak programmer if that makes any difference

any suggestions?
Shaun
amenjet
Posts: 237
Joined: Tue Jan 03, 2023 7:54 pm

Re: DIY Comms Link?

Post by amenjet »

Bumblemittens wrote: Thu Apr 27, 2023 3:20 pm Hey folks, so i built the comms link pcb, no magic smoke was released so that's a plus, however it is not seen by the organiser not even reporting a bad pak, i burnt the comms42.opk to the eprom as is, I understand that because of the design the data on eprom is scrambled, I'm not sure which comms image i should be using

As an after thought I'm burning the EPROM with EPROM programmer not datapak programmer if that makes any difference

any suggestions?
Shaun
Did you lay out a new Pcb from a schematic or did you use an existing PCb layout? The ROM is scrambled on the original Psion PCB so you will need a scrambled image. If you used another PCb layout then the scrambling could be the same, or different or there could be none. The PCBs I lay out don't have any scrambling. I also use flash chips instead of EPROMs, but that doesn't make much difference.

The ROM circuit on the top slot is separate from the serial circuit and also separate from the PSU circuit if there is one. So there are separate circuits that need to work and be tested. The ROM circuit has a lot of logic apart from the EPROM, and a fault in any of that logic will stop the ROM from being read and run correctly.

To burn the ROM using an eprom programmer you need a plain binary image with no headers and so on. The OPK file format has a header that will mean the programmed data is wrong, and as you say, there is no jumbling. Martin P sent me a jumbled image that I think he'll be happy me sending you if you need that, it depends on what circuit you are using.

Having had many failed top slot ROMs there is usually a 'bad pack' error or some other error, having no response is more unusual. I'd have a look at power or clocks to the ROM. A bad data or address connection usually leads to an error. That's just a guess, though, obviously.

Andrew
Bumblemittens
Posts: 32
Joined: Tue Apr 04, 2023 9:11 am

Re: DIY Comms Link?

Post by Bumblemittens »

Thanks Andrew, I'm using the schematic at this location https://www.jaapsch.net/psion/datasheets.htm it's the rs232 version not usb version, TBH I just enjoy building stuff, same goes for radio, nice if it works, if it doesn't then it's an education, I'm not new to PCB layouts, I've done plenty with my z80's, but yes, to have no response at all is puzzling, I've had bad Pak errors before and realised my mistake, oh well I'll just poke it with a stick

BTW eproms and through hole is what I had to hand at the time

Shaun
amenjet
Posts: 237
Joined: Tue Jan 03, 2023 7:54 pm

Re: DIY Comms Link?

Post by amenjet »

Bumblemittens wrote: Thu Apr 27, 2023 10:48 pm Thanks Andrew, I'm using the schematic at this location https://www.jaapsch.net/psion/datasheets.htm it's the rs232 version not usb version, TBH I just enjoy building stuff, same goes for radio, nice if it works, if it doesn't then it's an education, I'm not new to PCB layouts, I've done plenty with my z80's, but yes, to have no response at all is puzzling, I've had bad Pak errors before and realised my mistake, oh well I'll just poke it with a stick

BTW eproms and through hole is what I had to hand at the time

Shaun
OK, that is the original comms link and has jumbled data and address lines. I'll try to get the image you need to you. For some reason I can attach any files here, I always get a bad file extension error so I've put the image you need here:

https://github.com/blackjetrock/psion-o ... Comms_link

Andrew
Bumblemittens
Posts: 32
Joined: Tue Apr 04, 2023 9:11 am

Re: DIY Comms Link?

Post by Bumblemittens »

Thanks Andrew,

to add fuel to the fire, which is where this board might be going, I burnt the jumbled image to a Fujitsu MBM27C256A, no problems there, plugged the comms board into XP & pressed, on/clr, the organiser switched on, clicked once like it was sizing a pack but only clicked once and nothing on the display.

plugged the comms board into LZ, press on/clr, normal menu appears, press on/clr again, organiser clicks once and displays "out of memory, press space", hopefully shown in the image below if it displays, i'm not going to give up on this board but i guess in the end i'll just end up buying the propper comms link but in the mean time im going to continue tinkering with this one.

Pic isn't great, i had to reduce it from 5mb

Edit: OK, Nevermind, i screwed up and misslabeled some of the data line netports, that'll do it
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amenjet
Posts: 237
Joined: Tue Jan 03, 2023 7:54 pm

Re: DIY Comms Link?

Post by amenjet »

Bumblemittens wrote: Fri Apr 28, 2023 9:21 am Thanks Andrew,

to add fuel to the fire, which is where this board might be going, I burnt the jumbled image to a Fujitsu MBM27C256A, no problems there, plugged the comms board into XP & pressed, on/clr, the organiser switched on, clicked once like it was sizing a pack but only clicked once and nothing on the display.

plugged the comms board into LZ, press on/clr, normal menu appears, press on/clr again, organiser clicks once and displays "out of memory, press space", hopefully shown in the image below if it displays, i'm not going to give up on this board but i guess in the end i'll just end up buying the propper comms link but in the mean time im going to continue tinkering with this one.

Pic isn't great, i had to reduce it from 5mb

Edit: OK, Nevermind, i screwed up and misslabeled some of the data line netports, that'll do it
It looks nice.
Do you have any decoupling capacitors on there? They might help once it's up and running. Did you re-draw the schematic? If you post it someone might be able to spot something...
That sort of error is more like what you'd expect from some sort of addressing problem. So an improvement I'd say.

Is the organiser running off the supply from the adapter? The connector pinout is definitely the correct way round and ordered correctly?
Andrew
Bumblemittens
Posts: 32
Joined: Tue Apr 04, 2023 9:11 am

Re: DIY Comms Link?

Post by Bumblemittens »


It looks nice.
Do you have any decoupling capacitors on there? They might help once it's up and running. Did you re-draw the schematic? If you post it someone might be able to spot something...
That sort of error is more like what you'd expect from some sort of addressing problem. So an improvement I'd say.

Is the organiser running off the supply from the adapter? The connector pinout is definitely the correct way round and ordered correctly?
Andrew
Yes redrew or cloned if you like the schematic and layed it out to fit a through hole style, yeah its big and ugly but i figured it would be easier to troubleshoot rework through hole rather than SMD, no i forgot the caps in my excitement to get the gerbers away, i'll solder some direct to the pads on the back, looking back at my schematic i messed up the data lines going to the 74LS244, tracks cut now and i'll rewire it and see what happens and yes the organiser is running from a 10.5v supply, on a side note i didnt have any BAS16's so used 1N4148 and 2N3904 for the transistor, well see
Thanks for your help
Shaun
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