Connecting a viewdata terminal to a wifi modem?

Talk about non-Acorn classic computers/hardware/software here (including retro consoles)
Post Reply
tjewell
Posts: 3
Joined: Thu Sep 27, 2018 9:10 am
Contact:

Connecting a viewdata terminal to a wifi modem?

Post by tjewell » Fri Sep 28, 2018 11:50 am

Hi all, I've been reading with much interest the discussions on Viewdata services and wifi modems here. I've got a Tandata 1404 viewdata terminal with a serial connection that I'd love to connect to a wifi modem, and actually see it work again with the Glasstty service! But there's a problem - of course, the serial works at 1200/75 - and none of wifi modems go as slow as 75 baud. So what would be needed to support this? A new firmware? Or is there a technical limitation?

(Ps. this is part of a wider project at the Centre for Computing History to get our various Viewdata systems hooked up and actually doing something!)

User avatar
danielj
Posts: 6646
Joined: Thu Oct 02, 2008 4:51 pm
Location: Manchester
Contact:

Re: Connecting a viewdata terminal to a wifi modem?

Post by danielj » Fri Sep 28, 2018 12:42 pm

Hey there!

If they're hardwired to communicate 1200/75, it's problematic. If there's scope to configure the comms settings, the world's your oyster? Some of them have built in modems iirc?

Firmware wise it's just a question of rejiggling the firmware to respond to whatever commands the terminal is able to push down the line to connect and then do a telnet connect on the other end. That bit is fairly easy.

d.

User avatar
danielj
Posts: 6646
Joined: Thu Oct 02, 2008 4:51 pm
Location: Manchester
Contact:

Re: Connecting a viewdata terminal to a wifi modem?

Post by danielj » Fri Sep 28, 2018 12:49 pm

Further - just looking - it might be possible to coax it into playing at 1200/75 using the software serial library: https://github.com/plerup/espsoftwarese ... Serial.cpp

It won't be as reliable as the hardware library, but it's not going very fast so it might just work!

d.

tjewell
Posts: 3
Joined: Thu Sep 27, 2018 9:10 am
Contact:

Re: Connecting a viewdata terminal to a wifi modem?

Post by tjewell » Fri Sep 28, 2018 1:13 pm

I've managed to track down a manual here at the museum, and alas, 1200/75 is fixed (I'd been hoping for 1200/1200 as an option, but no). Software-serial looks interesting - you're right, it's very slow, so errors should be minimised. How would I go about using that?

Thanks all!

User avatar
danielj
Posts: 6646
Joined: Thu Oct 02, 2008 4:51 pm
Location: Manchester
Contact:

Re: Connecting a viewdata terminal to a wifi modem?

Post by danielj » Fri Sep 28, 2018 1:29 pm

I think you might have to rewrite the library in order to let it use the two separate baud rates, but once you've done that, the light-weight option is to tell the FreeFi-232 firmware on the stardot github to use software serial instead of hardware serial, and work on the basis that it's hard-coded to 1200/75. It'll need a bit of code-jiggling to do it, and you'll need a wifi-modem. Happy to send a version 2.4 PCB to the museum if you can nobble the rest of the bits to put one together?

d.

User avatar
1024MAK
Posts: 7994
Joined: Mon Apr 18, 2011 4:46 pm
Location: Looking forward to summer in Somerset, UK...
Contact:

Re: Connecting a viewdata terminal to a wifi modem?

Post by 1024MAK » Fri Sep 28, 2018 3:51 pm

If plan A above does not work, here are two other options.

Plonk a microcontroller in between. Use one with either two internal UARTs or one with one internal UART and use code to bit-bash another ‘serial port’. The microcontroller can then do the data speed adjustment.

Alternatively, if you have a spare old PC (386 or later) that has two RS232 serial ports (or you have suitable expansion cards to bring the total up to two serial ports). Then a relatively simple QBASIC (maybe even GWBASIC) program can auto boot from a MSDOS system floppy (or hard drive) and do the speed conversion.

Mark
Last edited by 1024MAK on Fri Sep 28, 2018 3:52 pm, edited 1 time in total.

guesser
Posts: 236
Joined: Mon Jun 26, 2006 9:21 pm
Contact:

Re: Connecting a viewdata terminal to a wifi modem?

Post by guesser » Fri Sep 28, 2018 5:28 pm

I was thinking if you wanted to have a display of a several terminals I'd get a small linux box with a serial port for each hidden away behind the display. It could run a server too so the entire thing was self contained, or route the connections out over the internet.

"Viewdata Rob" might be the person to talk to https://twitter.com/ViewdataUK
He's keen to get a public display of viewdata going (I think he wants a viewdata museum so he can get all the clutter out of his house!)
A web based teletext editor which can export as Mode 7 screen memory: https://zxnet.co.uk/teletext/editor

tjewell
Posts: 3
Joined: Thu Sep 27, 2018 9:10 am
Contact:

Re: Connecting a viewdata terminal to a wifi modem?

Post by tjewell » Sun Sep 30, 2018 10:28 am

Hi everyone, thanks for all your ideas!

Given that it's possible we're going to have a number of machines with the same challenge (plus, surely, we're not going to be the only people who'd like to get old Viewdata kit going?), I think the first thing to try is to build a wifi-modem that can actually support 1200/75, as that seems the neatest solution. @danielj, many thanks for the offer of a PCB. Do you also sell a finished board? Rewriting the firmware is a bit outside of my comfort zone, so I'm off now to read the various discussions about FreeFi on the forum while I wait for my personal Tandata to arrive. Any pointers on any other background reading I could do?

Thanks all!

Post Reply