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Upgrading serial port for higher speed / more midi stability


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Hi everyone,

I'm looking to mod the serial port on my Atari STE so I can reliably add 3 more midi channels.

I've looked into doing the RSVE mod but don't have access to a GAL programmer and can't seem to find any kits with preprogrammed GAL chips available.

I found this old thread here quite interesting:

That thread mentions that the GAL chip is a needless addition. It also mentions that higher modem speeds are impossible without an accelerator.

I have two questions if anyone is able to help:

1) Is there a serial port enchancer mod that does not require a programmed GAL chip?

2) Will a serial port enhancement to add additional midi channels to the ST require hardware acceleration in order to perform without excessive latency?


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I just about remember ST Format or ST Review having a DIY serial upgrade with parts available from Maplins (UK electronics retailer), you might want to flip through some of their back issues (it would be in the more recent, 40+ ST Formats if it is in there). I can't imagine that needed programmed gals. Iirc it was just doubled the speed (to 38400 ish), and required some soldering and possibly a track cut or two. 38400 is about the tops an ST will go without acceleration. I can't remember the speed the MIDI ports actually run at but vaguely recall they are about the same speed.

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Thanks for that response, some really useful information there.


I've had a quick flick through the contents pages of ST Format from issue 40 onwards but couldn't immediately spot anything that jumped (possible I missed something somewhere though, lot to go through!)


There is a 38400 mod on this page but instructions are both minimal and in German:


It does look like a relatively simple mod here with a few nand gates, some binary counters and a crystal. If anyone can help with a direct link to english instructions that'd be a massive help, I'll continue to look through those ST Formats and ST Reviews to see if I can find anything.


Edited by hasbab
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Hi, thanks for your message.


I am looking to add a midi expander to the serial port, something similar to C-Lab's Export to add additional midi channels, there are a number of DIY serial port solutions too.


The problem with all of these is that they introduce a significant amount of latency when dealing with 3 channel's worth of midi data and one of the reasons for this is the baud rate of the serial port.


Midi data requires a baud rate of 31250, I believe this is part of the reason that midi expanders for the serial port tend not to work very well and result in unreliable midi playback.


I did have some concerns about the software I was going to use (Notator) being able to access these increased speeds and was wondering whether running something like HSModem could set the serial port speed before using some midi expander in the serial port?

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You would need to run HS Modem to recognise the mod anyway, so that is essential (it would be worth doing even without the mod as the serial code in TOS is buggy). I suspect another problem will be how the MIDI program handles things. A few sequencers were set up to make sure the MIDI timing got preference over everything else, including the GUI, so whether they would be programmed to cope with the CPU requirements of pumping data out of the serial port as well I don't know.

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