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-- Visor & MIDI (http://discussion.visorcentral.com/vcforum/showthread.php?threadid=5431)

Has anyone succesfully used MIDI with the Visor through the built in serial port? People are using MIDI with the Palm, but the Visor has a different serial port implementation, so according to the miniMusic site there are some problems.

Anyone has information to share about this?

Of interest: a page about a Palm DIY MIDI interface.

Arthur

I don't have any actual experience, so I can't give you any definitive answers, but I can give you a few pointers.

The basic problems are: <UL TYPE=SQUARE><LI> The serial port on the Visor, is not standard:
* It uses TTL level signals instead of RS-232 level signals.
* It only has the Transmit-Data and Receive-Data pins (and Ground), no handshaking signals.
<LI>The Handspring Serial Cradle does the TTL to RS-232 conversion. However the circuit inside it draws its power from some of the Handshake lines driven by the Host computer. Other serial devices may not drive these lines. </UL>
The first page you referenced (miniMusic), appears to be fighting these problems. There has been a lot of discussion on using the Visor serial port with other devices, and the problems/solutions. You might want to search/read through some of them.

If I remember correctly, the MIDI interface is just serial, but using differential signals. The circuit on the second page you reference (PalMidi) appears to be just an RS-232 to differential signal conversion. But it draws some of its power from one of the serial signals (DB9 pin 8, which I don't remember what that is at the moment). I think that it would be easy to modify this circuit to: <UL TYPE=SQUARE><LI> Convert to/from TTL level signals. Probably by only changing a few of the resister values. <LI>Get its power from some other source. The Visor cannot really provide any power for the circuit.</UL>


[This message has been edited by potter (edited 06-02-2000).]

http://www.swivelsystems.com/products/sma.html

Have a look here, they're making a Visor to MIDI adapter, and a GREAT looking General MIDI module, although that's only for the Palm! I've written to them to ask them to develop a Visor version.. but I might have to buy a Palm IIIc in the meantime.

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The basic problems are: <UL TYPE=SQUARE><LI> The serial port on the Visor, is not standard:
* It uses TTL level signals instead of RS-232 level signals.
* It only has the Transmit-Data and Receive-Data pins (and Ground), no handshaking signals.
<LI>The Handspring Serial Cradle does the TTL to RS-232 conversion. However the circuit inside it draws its power from some of the Handshake lines driven by the Host computer. Other serial devices may not drive these lines. </UL>

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Originally posted by artelse:
Yes, would be easy. The docs mention that the Tx line can deliver 3.3V at 3 mA when the KBD line is kept low, but I have to look at the details.

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The question I had was that I was wondering what *inconsistancy* problems the miniMusic people were talking about..

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Can I ask why? Just wondering. It seems as if it would be only useful only to demo MIDI equipment.

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Eugene Hsieh
Editor, VisorCentral FAQ
Come visit my homepage.

To answer the last two posts, I'm interested in receiving MIDI data to control custom hardware in the Springboard slot. I was just hoping I didn't need to add a UART to the SB slot and it looks like the MIDI optocoupler and stuff can be powered from the Tx line.

I'm still wondering in what state the Tx line would be when KBD is held low. Would it be possible to still send data out, or is the output driver held in a permanent on state? Otherwise it would be possible to charge up a big cap, delivering the few mA to the MIDI interface logic.. just thoughts..

Tnx for the responses.

ae

To answer the last two posts, I'm interested in receiving MIDI data to control custom hardware in the Springboard slot. I was just hoping I didn't need to add a UART to the SB slot and it looks like the MIDI optocoupler and stuff can be powered from the Tx line.

I'm still wondering in what state the Tx line would be when KBD is held low. Would it be possible to still send data out, or is the output driver held in a permanent on state? Otherwise it would be possible to charge up a big cap, delivering the few mA to the MIDI interface logic.. just thoughts..

Tnx for the responses.

ae

after a research I ended up with this thread. has anyone successfullly come up with MIDI interface? if so, can anyone tell me how to do it or where to find related information? or should I wait till miniMusic to made SB module?

Springboard version on the way

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Originally posted by Welly
Have a look here, they're making a Visor to MIDI adapter, and a GREAT looking General MIDI module, although that's only for the Palm! I've written to them to ask them to develop a Visor version.. but I might have to buy a Palm IIIc in the meantime.

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