cs161fhn@sdcc10.ucsd.edu (Dennis Lou) (11/12/90)
On my room mate's Amiga, he plugs a little box into his serial port and voila! he's got MIDI in, out, and thru. Looking at the schematic, the box consists of a hex inverter and an optoisolator. On the RS-232 end, it only uses pins 2,3,7 and a +5V line (which is routed through 19 or 21). Why can't you do this on an IBM? What does the Roland MPU-401 have that a modified serial interface doesn't? What does the Amiga serial interface have that the IBM's doesn't? Can you roll your own sequencer/notation package using the serial port adapter? (please, let's not start a processor/architecture war here :-) -- Dennis Lou | "But Yossarian, what if everyone thought that way?" dlou@ucsd.edu | "Then I'd be crazy to think any other way!" [backbone]!ucsd!dlou +---------------------------------------------------- dlou@ucsd.BITNET cs161fhn@sdcc10.ucsd.edu | Woz went to my high school.
brian@ucsd.Edu (Brian Kantor) (11/12/90)
>From ucsd!brian Wed Sep 21 07:44:52 PDT 1988 If you're not a hardware type, this article may only be a bad temptation for you.... Recently I got interested in building a MIDI interface for an IBM PClone. A few years ago I'd have done for an S-100 system, but since PClones are the current hardware-hacker's junk computer, it seemed easiest to use one of them. Besides, they're cheap and easy to fix when you fry one. Parts are everywhere. Brief review of MIDI: Midi uses a serial asychronous protocol, running at 31.25kbit (31,250 baud). It sends a 10-bit frame consisting of a start bit, 8 bits of data (from LSB to MSB), and a stop bit. It uses an optically-isolated receiver and a 5ma current-sourcing transmitter in a current-loop configuration. Circuits are simplex (i.e., each pair of wires has a defined transmitter end [MIDI OUT/THRU], and a defined receiver end [MIDI IN]). Unlike every current-loop interface ever designed since Samuel F.B. Morse invented the land-line telegraph, MIDI idles in the marking ("1","on") state with no current flowing, and indicates a spacing ("0", "off") state by flowing current. (Yes, that means that it's inverted from everybody else's concept of current loop interfaces. Arrgh!) It uses 5-pin DIN jacks with the cable being twisted pair inside a shield. DIN pin 2 is the shield, pin 4 the + side of the source, and pin 5 the - side. Pins 1 and 3 aren't used, generally. The 8+2 bit frame is nearly identical to the serial interface used for personal computer data communications, although the electrical interface is quite different. Being of un-sound mind (PUN!) and thin wallet, I decided to see how I could build a MIDI interface for real cheap. Turns out that PClone serial interface adapter boards seem to be a drug on the market: there are lots of them out there for real cheap. So how to adapt one to MIDI? Watch: MIDI runs at 31,250 baud. You can't set a PClone async board to that baud rate - the closest you can get is 38,400 or 28,800. That's because the UART chip generates its baud rate by dividing a 1.8432MHz clock signal by a sixteen-bit number [in a register on the chip] to provide the baud rate clock at 16 times the actual baud rate. (For example, 38400*3*16=1843200, or 28800*4*16=1843200). Some Taiwan versions of the serial interface board use 18,432MHz crystals and a divide-by-ten chip to get the 1.8432MHz clock, while others just use a 1.8432 MHz crystal in the first place. 18MHz crystals are cheaper or easier to get, I guess. But if we change the baud rate generator clock to 2MHz, we can divide by 4 to get 500KHz, which is just right - because it's 16 times the MIDI baud rate. So: rip out the 1.8432 MHz [18.432] crystal and put in a 2.0 MHz [20 MHz] crystal. No problem: crystals are about $2 at the electro-junk store, and those hybrid oscillator modules that look like oversize tin chips are about $6. Real cheap. All you have to do is know how to un- and re-solder. The 8250 UART chip won't mind - its maximum baud rate generator clock frequency is spec'd at 3.1MHz. Ok, we've taken care of the baud rate. Now, the current loop. Early PClone serial cards had a current loop interface available by just reversing the large jumper header on the card (the small one changed it from COM1 to COM2 when you reversed it), but it's inverted from what MIDI wants, and later versions don't have current loop anyway. So we'll have to build an adaptor. The MIDI-OUT part is a breeze. RS232 swings from -12 to +12 on most PClone cards, since those voltages are available inside the machine. If we connect the - side of our PC-MIDI-OUT cable to signal ground (pin 7 on the 25-pin connector), and stuff a diode and a resistor in series between data out (pin 2) of the connector and the + side of the PC-MIDI-OUT cable, we've got it. The plus side of the diode (the end with the stripe on it) goes towards the cable so that current flows in the MIDI-OUT cable only when the port is at +12 volts, trying to send a zero. The diode is some el-cheapo silicon type like a 1N914 or 1N4148, and the resistor is 470 to 680 ohms -- it's just there to limit the current to around 5 to 10 ma like a good MIDI interface should. Put a 5-pin DIN plug on the other end of the cable, with the + wire going to pin 4, - wire to pin 5, and shield to pin 2, and connect the shield on the PC end to pin 1 of the DB-25, and you've got it. Voila! MIDI-OUT for your PC. MIDI-IN is a bit more complicated, but only slightly. First, you have to make sure that the serial card manufacturer provides + and -12 volts on pins 9 and 10 of the 25-pin connector. Most do. If not, they're certainly available on the card and you can install some wires (use wire-wrap wire) to route them to the connector. That taken care of, you need an opto-isolator chip. About $1 at the electo-junk emporium. I used a 4N37 chip because I had one, and it's a good choice, but almost any type with a phototransistor output should work fine. Connect a 4.7Kohm resistor between pin 10 (- voltage) and pin 3 (data in) of the 25-pin plug on the serial card. Connect the emitter lead (pin 4) of the chip to pin 3 on the DB-25, and the collector lead (pin 5) of the chip to pin 9 (+ voltage) of the DB-25. Connect the + wire of the PC-MIDI-IN cable to the anode (pin 1) of the opto-isolator chip, and the - wire of the cable to the cathode (pin 2) of the chip. The way this works is that the resistor keeps the serial card data in (pin 3) at -12 volts normally, which corresponds to an idle ("1") line. When current flows in the MIDI-IN circuit, the LED in the opto-isolator lights up, shines on the phototransistor, which switches on and provides +12 volts to the data in of the serial card, which reads it as a zero bit. Wrap the whole thing in electrical tape or something to make it sturdy, and you're done. If you are one of those souls blessed with a 9-pin instead of a 25-pin serial port, you'll have to figure out the pins for yourself, and find some way to get + and - 12 volts out the back. Maybe you could drill a hole in the card mounting plate and run the wires out. Note that shorting the 12 volt supplies to ground or to each other will probably fry something. Be careful! Software is something I'm still playing with, so I'll not include any here, except to show you how to set the baud rate to MIDI rate. Note that BASIC isn't fast enough; you'll have to use some compiled or assembled language that lets you frob with the ports directly. You've only got ~320 microseconds to grab an incoming MIDI byte, so you can't waste time. Note also that PC interrupts are really SLOW, so you may be better off with polled port I/O. This fragment of C code assumes that your interface lives at COM2 at address 2F8 in the PClone. Clearly you could put it elsewhere. outportb(0x2fb, 0x83); /* select baud rate divider latch */ outportb(0x2f8, 4); /* low byte of divider = 4 */ outportb(0x2f9, 0); /* hi byte of divider = 0 */ outportb(0x2fb, 3); /* deselect baud; 8-bit no parity mode */ >From this point on, you can read port 2FD for the serial port status, and read/write port 2F8 to receive and send MIDI data. The rest is up to you. Don't fry anything expensive. Enjoy! Brian Kantor UC San Diego "There is more harmony in films than in life." - Francois Truffaut P.S.: it's virtually certain that commercial MIDI software packages can't use this interface, since it'll be at the wrong address at least. Sorry 'bout that.
dgold@basso.actrix.co.nz (Dale Gold) (11/13/90)
Quoted from - cs161fhn@sdcc10.ucsd.edu (Dennis Lou): > On my room mate's Amiga, he plugs a little box into his serial port > and voila! he's got MIDI in, out, and thru. > [...] > Why can't you do this on an IBM? What does the Roland MPU-401 > have that a modified serial interface doesn't? A friend of mine has built an IBM interface based roughly on my homemade Amiga box. The problem is that all (?most?) of the good IBM software is designed for the MPU-401, which has a lot of built-in features. Don't ask me what they are! :-) My friend is going to write his own s/ware, so for him, it's not a problem. > What does the Amiga serial interface have that the IBM's doesn't? Basically, nothing. My old A1000 has a source of power through the serial port - I think this was eliminated in the 500-3000 range. Otherwise, there's nothing unusual in the Amiga port. > (please, let's not start a processor/architecture war here :-) > No way, mate! Cheers, Dale -- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | | Critics can't even make | | dgold@basso.actrix.co.nz | music by rubbing their back | | | legs together. - Mel Brooks | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
herbie@bruce.cs.monash.OZ.AU (Andrew Herbert) (11/14/90)
In <4840.tnews@basso.actrix.co.nz> dgold@basso.actrix.co.nz (Dale Gold) writes: [talking about rs-232 to midi interfaces] >A friend of mine has built an IBM interface based roughly on my homemade >Amiga box. The problem is that all (?most?) of the good IBM software >is designed for the MPU-401, which has a lot of built-in features. Don't >ask me what they are! :-) My friend is going to write his own s/ware, so >for him, it's not a problem. >[...] Isn't there a problem getting an ibm serial port to spit out 31.25kbps as required by midi? Andrew
rzi@philpav.tds.philips.se (Roman Zielinski) (11/14/90)
In article <4840.tnews@basso.actrix.co.nz>, dgold@basso.actrix.co.nz (Dale Gold) writes: > Quoted from - cs161fhn@sdcc10.ucsd.edu (Dennis Lou): > > [...] > > Why can't you do this on an IBM? What does the Roland MPU-401 > > have that a modified serial interface doesn't? > > [...] A simplest MIDI-interface can be built as an UART plus opto-isolator working in 31kb/s speed. Normal UARTs in PCs can work up to 19.2kb/s (You can force them to higher speeds, but.... what happens if your CPU will be too busy to handle all interrupts from UART?) MPU401 is a Motorola 6800-based system (not just an UART shifting out/in data to/from the line). It is very clever card performing all timing work. It also keeps track on measures, tempos, metronome bit, etc MPU and application use a handshaking protocol so you can transfer data and events in both directions simultanously. For example, from application you send events tagged with time-to-next event, like: time-to-next-event <event> <event-data> 05 ch=1 tone-on tone velocity 25 ch=2 tone-on tone velocity 36 ch=5 program-change prog 55 ch=1 tone-off tone measure measure 01 ch=2 tone-off tone Due the timing facilities the application can work quite asyncronously to the hardware, and it cannot be done with a pure UART system. Roland has a techn spec for $5-10, it is about 70-80 pages... +-------------------------------------------+ _--~--_ | Roman M. Zielinski | ---- / \ ---- | Philips Tele & Data System AB | ---- ( |^^^| ) ---- | S-115 84 Stockholm, Sweden | ---- \ \ / / --- | tel +46 8 782 1373 | |=====| +-------------------------------------------+ |=====| | NET ADDR: rzi@pav.tds.philips.se | |=====| +-------------------------------------------+ ~~U~~
helin@vehka.uta.fi (Mikko Helin) (11/14/90)
In article <505@philpav.tds.philips.se> rzi@philpav.tds.philips.se (Roman Zielinski) writes: > >MPU401 is a Motorola 6800-based system (not just an UART shifting out/in data >to/from the line). It is very clever card performing all timing work. It also >keeps track on measures, tempos, metronome bit, etc > MPU401 can't handle Song Position Pointers (SPPs), so the only way is to use MPU in UART mode. All sequencer software that is claimed to understand SPPs does this. In my opinion, Voyetras VAPI is better standard than MPU401 in IBM compatibles (I mean software drivers). By the way, has anybody there written VAPI driver for modified RS-232 card or knows something about it? Plese tell us others! > >Due the timing facilities the application can work quite asyncronously to >the hardware, and it cannot be done with a pure UART system. > It has been done anyway. -------------------------------------------------------------- MIKKO HELIN FINLAND INET: helin@vehka.uta.fi --------------------------------------------------------------
jones@sdd.hp.com (Christopher Jones) (11/15/90)
In article <4840.tnews@basso.actrix.co.nz> dgold@basso.actrix.co.nz (Dale Gold) writes: >Quoted from - cs161fhn@sdcc10.ucsd.edu (Dennis Lou): >> On my room mate's Amiga, he plugs a little box into his serial port >> and voila! he's got MIDI in, out, and thru. >> [...] >> Why can't you do this on an IBM? What does the Roland MPU-401 >> have that a modified serial interface doesn't? > >A friend of mine has built an IBM interface based roughly on my homemade >Amiga box. The problem is that all (?most?) of the good IBM software >is designed for the MPU-401, which has a lot of built-in features. Don't >ask me what they are! :-) My friend is going to write his own s/ware, so >for him, it's not a problem. > > >Cheers, Dale I've also designed and built an IBM-Midi interface which "uses" the serial port to operate. Uses in quotes, because I'm not using the IBM serial port's hardware, but rather its COM2 port address and protocol. The interface card connects directly to the XT bus, and employs a 12MHz 8051 microcontroller to UART and timestamp MIDI data. I realize that this isn't exactly what Dennis was talking about, but in order to accomplish that (as someone has mentioned), you'd have to change the oscillator on the IBM serial port's hardware, or build an intelligent serial<--->serial converter, perhaps with the MCS-51 chip. /ctj
pete@wlbr.IMSD.CONTEL.COM (Pete Lyall) (11/15/90)
Actually, I use Sequencer Plus MKIII with an OP-4001 and it syncs very
nicely to Song Position Pointers. I understand that it cannot digest
MTC (Midi Time Code.. an addition to the MIDI SPEC that MIDI-fies
SMPTE frame data)...
Pete
--
Pete Lyall Contel Corporation
Compuserve: 76703,4230 OS9_Net: (805) 375-1401 (24hr 300/1200/2400)
Internet: pete@wlbr.imsd.contel.com UUCP: {hacgate,jplgodo,voder}!wlbr!pete drfoam@watcsc.waterloo.edu (Dennis Henry) (11/18/90)
Thanks to all those who responded to my question. Here is a summary of the Email I got (less the article from Brian Kantor which has already been posted). One other note. A couple of people have mentioned a BYTE project for a MIDI interface. I have located it (JUNE, 1986) and also a MIDI recorder program for the Roland MPU-401 in the BYTE IBM Special Issue Volume 10, Number 11, 1985. Dennis Henry ========================================================================== From maytag!sprite.Berkeley.EDU!shirriff Tue Nov 6 20:49:14 1990 Date: Tue, 6 Nov 90 16:01:59 PST From: maytag!sprite.Berkeley.EDU!shirriff (Ken Shirriff) To: drfoam@watcsc.waterloo.edu Subject: Re: MIDI Interface Newsgroups: sci.electronics In-Reply-To: <1990Nov6.120535.10850@watcsc.waterloo.edu> Organization: University of California, Berkeley In article <1990Nov6.120535.10850@watcsc.waterloo.edu> you write: >A friend of mine has embarked on a project to interface his computer >to some MIDI instruments. He wishes to build the hardware and to >write the software. Try asking in rec.music.synth. You should be able to get lots of advice there. Ken Shirriff shirriff@sprite.Berkeley.EDU "There are 2 basic truths, never fight a land war in Asia and never go against a Sicilian if death is on the line." From maytag!unix.cis.pitt.edu!fmgst Wed Nov 7 00:34:44 1990 Date: Wed, 7 Nov 90 00:14:58 -0500 From: Filip Gieszczykiewicz <maytag!unix.cis.pitt.edu!fmgst> To: drfoam@watcsc.waterloo.edu Subject: Re: MIDI Interface Newsgroups: sci.electronics In-Reply-To: <1990Nov6.120535.10850@watcsc.waterloo.edu> Organization: The Last Jedi Greetings. Look in Byte. I CLEARLY remember (maybe even have) an article about MIDI, how to build a card for IBM, and sample software listings. It has diagrams for the board, in all not a bad project. Listings were in basic I think. If your friend is doing this for IBM, e-mail me for more info... Take care. -- _______________________________________________________________________________ "The Force will be with you, always." It _is_ with me and has been for 10 years Filip Gieszczykiewicz "... a Jedi does it with a mind trick... " ;-) FMGST@PITTVMS or fmgst@unix.cis.pitt.edu "My ideas. ALL MINE!!" From maytag!oasys.dt.navy.mil!curt Wed Nov 7 11:29:17 1990 Date: Wed, 7 Nov 90 10:35:18 EST Newsgroups: sci.electronics References: <1990Nov6.120535.10850@watcsc.waterloo.edu> From: maytag!oasys.dt.navy.mil!curt (Curt Welch) Subject: Re: MIDI Interface To: drfoam@watcsc.waterloo.edu (Dennis Henry) Cc: curt@oasys.dt.navy.mil In article <1990Nov6.120535.10850@watcsc.waterloo.edu> drfoam@watcsc.waterloo.edu (Dennis Henry) writes: >A friend of mine has embarked on a project to interface his computer >to some MIDI instruments. He wishes to build the hardware and to >write the software. They talk a lot about this in rec.music.synth and rec.music.makers. You might try posting your question their also. You should also specify what type of computer your friend has. >Any information or references to information on the hardware interface >and the data formats would be much appreciated. Your friend should get a copy of the MIDI spec. The people in rec.music.synth can give you the address to write to. There is an organization in CA (West Hollywood I think) that is responsible for the MIDI spec. Curt Welch curt@oasys.dt.navy.mil Code 3531 David Taylor Research Center (A Navy Lab) Bethesda, MD (301) 227-1428 From maytag!flute.cs.uiuc.edu!totty Wed Nov 7 21:45:08 1990 Date: Wed, 7 Nov 90 20:02:59 CST From: maytag!flute.cs.uiuc.edu!totty (Brian Totty) To: drfoam@watcsc.waterloo.edu Subject: Re: MIDI Interface In article <1990Nov6.120535.10850@watcsc.waterloo.edu> you write: > A friend of mine has embarked on a project to interface his computer > to some MIDI instruments. He wishes to build the hardware and to > write the software. I just built an RS232 -> MIDI interface for my Yamaha synth. I can provide some info about my very sub-optimal hardware and a bit about the MIDI protocol if you send some specific questions. / Brian Totty o o /__ __ o 1304 W. Springfield Avenue o / / / / Urbana, IL 61801 \_/ "We have corn in /__/ / / totty@cs.uiuc.edu Massachusetts too!" From maytag!VAX1.Mankato.MSUS.EDU!MARAUDER Sat Nov 10 15:00:07 1990 Date: Sat, 10 Nov 90 10:57 CST From: Joseph Arlanda Enterprises <maytag!CUNYVM.CUNY.EDU!MARAUDER%VAX1.Mankato.MSUS.EDU> Subject: Midi interface To: drfoam@watcsc.waterloo.edu X-Envelope-To: drfoam@watcsc.waterloo.edu X-Vms-To: IN%"drfoam@watcsc.waterloo.edu" There is a post script file in the sumex-aim archives that is a one-instrument midi interface. It is under info-mac/sounds/program @ sumex-aim.stanford.edu. Hope this information helps. -Todd Hartman ========================================================================== drfoam@watcsc (Dennis Henry)
dgold@basso.actrix.gen.nz (Dale Gold) (11/21/90)
Quoted from - herbie@bruce.cs.monash.OZ.AU (Andrew Herbert): > In <4840.tnews@basso.actrix.co.nz> dgold@basso.actrix.co.nz (Dale Gold) writes: > > [talking about rs-232 to midi interfaces] > >A friend of mine has built an IBM interface based roughly on my homemade > >Amiga box. > >[...] > > Isn't there a problem getting an ibm serial port to spit out 31.25kbps > as required by midi? > I believe so. I know he had to do some fiddling with the clock speed or something. I'll ask him and post anything useful he might have discovered. -- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | | Critics can't even make | | dgold@basso.actrix.gen.nz | music by rubbing their back | | | legs together. - Mel Brooks | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
shri@ncst.ernet.in (H.Shrikumar) (11/26/90)
In the discussion on rs232-to-midi interfaces ...
dgold@basso.actrix.gen.nz (Dale Gold) and
herbie@bruce.cs.monash.OZ.AU (Andrew Herbert) contribute:
dgold> A friend of mine has built an IBM interface based roughly on my homemade
dgold> Amiga box.
dgold> [...]
herbie> Isn't there a problem getting an ibm serial port to spit out 31.25kbps
herbie> as required by midi?
dgold> I believe so. I know he had to do some fiddling with the clock speed or
dgold> something. I'll ask him and post anything useful he might have discovered
I have been thru this stage, so I thought I'd answer this FAQ...
The standard 8051 (?) Serial interface in the IBM PC, using a 1.84 MHz
Xtal can generate 19.2Kbps or 38.4Kbps. But to get it to generate
the MIDI baud rate, what needs to be done is a "simple" (if you
are adept with a soldering iron) change of the crystal on the serial
interface board to a 1MHz or 2 MHz unit. This will enable the software
to set it to 31250 bps by doing what you'd normally do to set it at
38.4Kbps or 19.2Kbps respectively.
If the serial clock is generated from the system clock on the
mother board (if serial interface is on mother board) ... then it is
more difficult.
Having done this, you get a +-12V, 31250 baud serial stream, set to
8bits, no parity. An external box (like the ones with an Amiga) will
convert the +-12Volt to a 5mA current loop for output, and an opto
for the input. Done. This method works, only needs careful soldering.
Now I have a question ... could some one describe to me what the
Roland MPU-101 looks like ... is it a card you plug into the PC, or
is it a box you connect to a normal RS232 port ?
If the latter, I am sure you can connect a MPU101 to a SUN or
pretty much any computer, as long as you write the software for it.
Anybody used a MPU101 with anything but an IBM-PC ?
TIA.
-- shrikumar ( shri@ncst.in )