djg@well.UUCP (David Julian Gray) (03/25/86)
In article <1885@hammer.UUCP> andrew@hammer.UUCP (Andrew Klossner) writes: >I'd like to use my lap computer (Epson PX-8) as a patch librarian, but >all it speaks is 9600 baud RS232. Does anyone make a MIDI <-> RS232 >converter? A FIFO between fast MIDI input and slow RS232 output should >be enough to prevent overrun. Right, Andrew - going from 9600 bps of your Epson to the 31.2K bps of MIDI will require some hefty, and preferably "intelligent" buffering. Luckily there exists just such a black box: MIDIC from Hinton Instruments 168 Abington Road Oxford, OX1 4RA England It comes with either a 2K or 10K buffer (at ~$300 and ~$360 respectively). I know of no one with personal experience with these devices - most knowledgable MIDI users and developers I've discussed RS-232 <==> MIDI with are quite disparaging. I think that's due to a touch of laziness (and the fact that anyone using MIDI professionally and heavily gets a dedicated MIDI port). The Epson PX-8 is Z-80 based, no? David Droman in "Exploring MIDI" describes a MIDI interface and software developed for a Z-80 based Kaypro, using the Z-80 PIA chip. Real World: David Julian Gray Computers & Music 1989 Junipero Serra Blvd. Daly City, CA 94014 415 994-2909 UUCP: {apple,dual,ptsfa,hplabs,netisun}!well!djg
jer@peora.UUCP (J. Eric Roskos) (03/31/86)
> Right, Andrew - going from 9600 bps of your Epson to the 31.2K bps of MIDI > will require some hefty, and preferably "intelligent" buffering. ... most > knowledgable MIDI users and developers I've discussed RS-232 <==> MIDI > with are quite disparaging. I think that's due to a touch of laziness > (and the fact that anyone using MIDI professionally and heavily gets a > dedicated MIDI port). As I mentioned briefly back when I wrote my series of postings on the MIDI interface for the Macintosh, back before I bought DMCS, I had built an RS-232 to MIDI interface. The reason I haven't yet posted the diagrams for it is that I used a single-board computer that seems not to be manufacutured any more, so for it to be useful you'd have to put together your own, though I think it should be possible to do it with just a 6801, an EPROM, a small external RAM, and the RS-232 line drivers. (I also used a PIA to generate the MIDI signals, but you should be able to do that with the parallel output lines on the 6801 since only 2 are required.) However, other than the software (which requires precise timing loops), it is very *easy* to build such an interface, and furthermore it works well. I have heard suggestions that the slower baud rate of the RS-232 port might cause delays that might affect the sound; however, I've found this wasn't the case -- if you think about it, it is almost impossible to press a set of keys at exactly the same time anyway, so it could be argued that the delays, if they were audible, would add more "realism". It doesn't require any particularly intelligent buffering, though; I used a simple 512-byte circular buffer. Coming out of the computer, the rate of character transmission is limited by the RS232 port, so you can't overrun your MIDI port. Going the other way, you rarely have incoming data at anywhere near a rate that would overrun 9600 baud for a sustained time due to the fact that the human performer can't move that fast... you might be able to do it by moving the "pitch bend" control continuously for a long time, though. So my point is, if you are thinking about building such a device, don't be discouraged by "disparaging" comments about the performance. It works fine. [I do apologise to the people who wrote and wanted a copy of the diagrams for it... I tried to find the manufacturer of the single board computer, but so far have been unsuccessful -- it was made by a group of EE grad students who had a small company; they advertised in Byte a couple of times -- I'm still planning to do a general block diagram of it, along with posting the software, however. I've also thought about doing a Byte article on it, which would probably be a better approach given the need for drawings, etc.] -- E. Roskos