VOGONS


First post, by RichB93

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Hi all,

I noticed that the SB-55 has a test mode, whereupon if you put the unit into standby mode and press and hold the PROG+SET+RWD+FF buttons, you see 'tSt' appear on the display. According to the manual you should see SEr on the display for service mode - it seems that the service mode requires a specific diskette that wasn't mentioned in the service notes.

It turns out, in this mode, the SB-55 will load program code from the disk and execute it. It has a NEC V25 CPU which is 8086 compatible too.

With this in mind, I created a cool little demo - a game of snake for the SB-55 and SoundCanvas. Currently a remote control is also required to control the game.

Write the attached image to a disk, put the device into tSt mode, and insert it.

Controls are as follows:
Play - start game
Stop - pause game
Song down - left
Song up - right
Tempo up - up
FF - down

I'll eventually add controls via the front panel controls so that a remote control won't be required and polish this a bit more.

Video of it in action is here: https://www.youtube.com/watch?v=uAvGC3Sdd4M

EDIT: Version 2 added - adds front panel controls, a sound effect when the apple is eaten, front panel LEDs are now used, and also the ability to reboot the device by pressing the power button.

Last edited by RichB93 on 2026-09-02, 15:45. Edited 2 times in total.

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Reply 1 of 5, by wierd_w

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A more interesting use, would be to add novel programmable softsynth programs to it, IMO.

It wont have much ram, and the CPU is a bit weak compared to modern devices, but it should still be able to do interesting things.

Reply 2 of 5, by RichB93

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wierd_w wrote on 2026-08-31, 22:26:

A more interesting use, would be to add novel programmable softsynth programs to it, IMO.

It wont have much ram, and the CPU is a bit weak compared to modern devices, but it should still be able to do interesting things.

I think you overestimate the capabilities of the device.

There's around 25.5 kilobytes of useful RAM, and there is no audio output on the device - the only I/O is the floppy drive and the MIDI ports.

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Reply 3 of 5, by wierd_w

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It could still do interesting things, like produce dynamic drum rythms based on some input on its input port, or be used to dynamically intercept and manipulate inbound midi messages based on some rules, before sending them out again.

You dont *need* a large amount of ram for a serial transfer buffer, especially if there's no operating system to speak of.

Reply 4 of 5, by RichB93

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Totally agree - I was thinking of creating some kind of arpeggiator. But that’s quite different to a soft synth.

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Reply 5 of 5, by wierd_w

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Dynamic accompanyment generation (say, analysis of note pattern progression over a period of measures, used to generate 'harmonic parts' to accompany the provided musical notation sent on the input port) would be a synth of 'a sort'.

Might be accurate to call that a 'polyphony expander' or something though.

It would introduce nontrivial delay though. (needs to collect, then keep, a musical sample period to work with to derive accompanyment candidates with. that's several seconds of realtime delay)

Just spitballing ideas.