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User Port Switching

Posted: Tue Nov 07, 2017 4:42 pm
by jubber
Usual aplogies if this subject has often been broached before - but I couldn't find anything about it here.

I've got an MMC and some analogue joysticks, not to mention a couple of other bits and pieces lying around that could make use of the user port. Is there any suggested method to connect them both at the same time? I suppose I could run some extra wires from the user port and just attach them to something the joysticks can plug into (perhaps the user port used a standard connector that I can find on ebay) but I'm wondering if a switch would be necessary so that the two signal paths don't interfere with each other. Has anybody done this sort of thing?

Many thanks,

Robin.

Re: User Port Switching

Posted: Tue Nov 07, 2017 5:04 pm
by DutchAcorn
There have been a few threads on this. I searched for "user port switch" and found a few.

One of them here: viewtopic.php?f=3&t=5488

Re: User Port Switching

Posted: Wed Nov 08, 2017 12:40 am
by sweh
Alternatively, you build a 2nd (and 3rd) user port: https://sweh.spuddy.org/Beeb/2nd_User_Port/

It'll be at a different memory location but will work for many use cases if you can modify the code. I have UPURS working from it, for example.

Re: User Port Switching

Posted: Wed Nov 08, 2017 1:41 am
by jubber
Thanks very much - crucially I left out "switch" when searching on these forums.

From the looks of it, I'll need some ribbon cable, a couple of male 25 pin connectors (idc, for cable), a 20 pin female connector (idc, for cable), and the parallel printer switch box for everything to connect to.

I'll find them online and post them up if I get it working - the previous post could do with a bit more info for non-engineers like myself.

Cheers,

Robin.

Re: User Port Switching

Posted: Wed Nov 08, 2017 1:45 am
by jubber
sweh - thanks for the suggestion - that looks really really hard!

Good work on figuring out how to build that. I may be going the same route as your initial switch box attempt. If I can get joystick and mmc working I'll be happy. One question - you mention having to turn off the computer between switching - is there a risk that blithely switching the user port can damage the machine?

Cheers,

Robin.

Re: User Port Switching

Posted: Thu Nov 09, 2017 1:02 am
by sweh
I don't recall needing to turn off, but pressing control-break was needed to force the MMC ROM to reset.

If you build a switch box then you can probably start with it set to MMC mode, load the game, then switch to joystick mode. But at that point it's unlikely you'd be able to switch back to MMC mode 'cos the joystick routines would have reprogrammed the 6522 so you wouldn't be able to save game or similar.