bennett@galois.esd.sgi.com (Jim Bennett) (12/14/90)
I basically got two different responses to my query. In case you have forgotten, this is what I posted: I am looking for a MIDI interface box that could be attached to an arbitrary computer, via an RS232 interface, for example. Does anyone out there know of such a device? The two suggestions were: > From weissman@pianoforte Fri Nov 30 14:09:29 1990 > > You will probably get lots of people telling you about the Hinton > MIDIC. This is a box made by Hinton Instruments, a very small company > in England. It does all sorts of good things. It also costs a lot (~335 pounds). > > If you want more info on the MIDIC, let me know. I used one a fair > amount in a previous life. > > - Terry and > From lstead@iris.bellcore.com Sat Dec 1 15:07:19 1990 > > I'm so glad you asked! > > Key Electronics 800-533-midi makes a "midiator" which does the right > thing, rs-232 to midi. I have one hooked up to my vgx 340. Costs about > $200 bucks, and make sure you order the power supply. > > It has a very nice feature - using the modem control signals, you can > switch your single rs-232 stream to FOUR different midi outputs, which is a > major win if you have alot of stuff. Even more important, it > implements a simple flow control protocol so you can run the serial > line at 38kbaud without overflowing on output, again using a modem > control signal. Other people also suggested Key Electronics. I also got this interesting response, that didn't really address the question I was asking (or at least the question I meant to ask). I found it very informative, however, and decided to include it here for the hardware hacks: > From: Stan Kalinowski <stank%anvil.wv.tek.com@RELAY.CS.NET> > Organization: Tektronix, Inc., Wilsonville, OR > > I won't try to list the manufacturer's, but I'll explain the problem > so that you know what your're up against. Checkout Keyboard and > Electronic Musician magazine for interface ads. > > Basicaly, there are two problems you will need to solve in the > interface. MIDI runs at 31250 Baud and it is a current loop that is > isolated with opto-couplers. If you can coax your serial interface to > run a 31.250 Kbaud, then all you need is an RS-232 to MIDI level > shifter box. The design of this interface box is very simple. It has > has an opto-coupler (6N-138), buffer (74LS05), and a couple of RS-232 > to TTL level translators (MC1488 and MC1489). You probably have the > parts in your engineering stockroom. Electronic Musician has run > articles describing how to build such a box, one was in the Dec. '88 > issue, I can look up the date of the other one if you're interested. > > If you can't generate 31.250 KBaud then there are three possible > solutions: > > 1. Modify your serial port to use a different clock. (You > might be able to find 1Mhz or 2Mhz somewhere on the board, > these can be divided down to 31.250 KBaud by the Uart. > > 2. Use the external clock pin on the serial port. If your > serial port complies with the RS-232 spec, the external > clock pin should be fed into the external clock input of > the UART. You can then feed in the appropriate clock and > devide it down with the Uart. I believe the Mac interfaces > work this way, but I am not sure. This assumes, of course, > that you can reprogram the Uart to use the external clock, > I think this means hacking the driver. > > 3. Get an interface that takes 38.4 Kbaud serial in, decodes > it, and then transmits it at 31.250 KBaud. The problem > with this kind of Uart to Uart interface is that they don't > provide much (if any) buffering and so it is easy to loose > data. Midi does not have a flagging scheme and some of > system exclusive messages involve large blocks of data, > these tend to fail with the Uart to Uart type of adapter. > I think I might still have some on-line notes that describe > how to build one of these. It was written by Brian R. > Smith, but I didn't try to build it because it seemed > conceptually flawed to me. (i.e. no FIFO buffer.) If > your're interested, I can send them via e-mail. (If I can > figure out where/if I archived them.) > > There is a company called Key that makes a serial adapter for Unix > machines, but it overly expensive in my opinion. It costs about $240. > I have heard rumors that this box might also require a special side > channel to control it, the side channel is driven by a Centronics > style printer port. If that rumor is true, it is both worthless and > expensive. > > stank > > > > > > -- > US Mail: Stan Kalinowski, Tektronix, Inc., Network Displays Division > PO Box 1000, MS 60-850, Wilsonville OR 97070 Phone:(503)-685-2458 > e-mail: {ucbvax,decvax,allegra,uw-beaver}!tektronix!orca!stank > or stank@orca.WV.TEK.COM