8 pin "null" round modem cable wiring help needed


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Old 06-09-16, 09:27 AM
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8 pin "null" round modem cable wiring help needed

Hi everyone,

I'm new to this forum and hoping someone can offer some insight. i have two devices that are able to network together using a "null" modem cable. it would look physically like this:

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however everywhere i look, i find "printer" cables.. which are wired 1 to 1.. what I need is a "null" modem cable which has some wires crossed to allow a different form of communication.

This is for a Mark of the Unicorn Midi Time Piece AV. they have the ability to network two of them together.. also note that they use this round connection on both ports.. however they are also called RS422 cables.. but in all my research i come up with FS422 cables looking like this:

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I've reached out to MOTU to ask if they know something about this. However maybe this idea of a null cable is known by someone who could help me understand how to wire things up correctly.. i have two of these "printer" versions of the cable which do not work because of the wiring.. they simply do nothing to communicate with each other.

Any tips / advice would be super welcome!
 
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Old 06-09-16, 11:31 AM
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The round cable you show is a PS2 keyboard or mouse cable. It is not generally used for RS232 or RS422 serial communications which is why you won't find a null modem configuration for it.

We could probably tell how to make one from a standard cable, but would have to know the signal pinout for the Midi. Perhaps the pinout is described in the midi manual?
 
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Old 06-09-16, 11:44 AM
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it's not midi.. it's RS422.. here is the back of the device i'm talking about. see the cable id below the two ports. one is for the "mac" or "pc"..
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this isn't ps2 either. ps2 looks like this with the big plastic pin space preventing other similar shaped items like the RS422 from working with it:
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So yea it's an odd duck of a cable from a looooong time ago..
 
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Old 06-09-16, 11:48 AM
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additionally, this url actually offers a promising number of options, but which one of those null cable configurations is what works with the MOTU MTP AV

RS-232 and RS-422

I'm waiting to hear back from them about this. they are looking into it.
 
  #5  
Old 06-09-16, 12:14 PM
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How old is that thing? Looks like an Appletalk or SUN keyboard/mouse connector.
 
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Old 06-09-16, 12:52 PM
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yes it is "appletalk" which i'm trying to find now. i did find this:

QTALK8 Appletalk Compatible Network Starter Kit | eBay

I'm contacting the seller to see if they can verify it will serve my needs.

this is what computers like the Mac Classic (which I have as well from 1990!) for printer / modems. I think the main thing is that the cable has to be a null cable which IIRC means it's setup to allow a different kind of "back and forth" communication that isn't what is used with things like printers where information is pretty much one way.. but modems have to send / receive information so they use a different configuration.

So what makes this unique is that it

1. must be serial, not parallel.
2. round on both ends not a DB9 on one end (which i have found)
 
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Old 06-09-16, 01:26 PM
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So this may be what you need - a crossed LocalTalk cable:
Opentip.com: IEC M1527 Apple Mac&#8482 Mini Din 8 Male to Male Local Talk Cable 6'
 
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Old 06-09-16, 01:40 PM
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yes i think that it! i was looking at this fella (a few dollars more)

Vintage Appletalk Connector Kit in Box Complete No Tray Instructions Unopened | eBay

but yea i think you nailed it. i also found this one
6 ft. Apple/Mac Serial Cable - MiniDin8 | CableWholesale

but i think yours is very explicit in that it's used to connect to devices to talk back and forth and a few dollars cheaper

Thanks!
Caleb
 
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Old 06-09-16, 01:44 PM
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@astuff i've ordered that one.. let's hope it works!

Thanks,
Caleb
 
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Old 06-10-16, 04:38 AM
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That's called an 8-pin DIN RS-422 cable. Here are the pinouts. "Legend" is RS422; the right column is RS232. A null cable would swap pins on one end: TX+ to RX+, TX- to RX-.

Attachment 67132
 
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Old 06-10-16, 04:39 AM
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that's cool, so now the key is to know how to make a serial ( with crossover) when both ends of the cable need to be the round 8 pin.

also i did get word back from the Appletalk connector kit and thankfully the seller provided an extra picture when i emailed him and it was the wrong type of connector.. but the one i ordered looks good..

"The M1527 is designed to connect to Apple Peripherals which require a crossed wiring. The M1527 is not a straight through cable, for a straight through wiring, see our M1521."

Opentip.com: IEC M1527 Apple Mac&#8482 Mini Din 8 Male to Male Local Talk Cable 6'

that quote couldn't be more appropriate, but i won't know till i hook them up.

the two that i bought recently (using a multimeter) were like the other "M1521" it's a 1 to 1 for the pin configuration
 
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Old 06-10-16, 04:46 AM
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@rick when I tried to click on the attachment.. the attachment was "Invalid Attachment specified. If you followed a valid link, please notify the administrator"

but i think i follow you based on the text you wrote. thanks! I have another imagine I want to reference. would this be a good legend? it seems a bit more complicated than your explanation.. btw this configuration here is what i rewired my cable too and it didn't work.. it made some lights light up but not in a good way kinda crazy.. hopefully it didn't do any damage to the devices. I don't think these network ports were sending any "power" over them.

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  #13  
Old 06-10-16, 09:25 AM
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part12-

I believe RS422 only refers to the electrical characteristics of a balanced pair Ė such as 2 wires for transmit data and 2 for receive data etc. Everything else for the connection, connector type, pin assignments, etc. comes from other standards. So RS422 doesnít tell you a lot.

Looks like the ď8-Pin Mini DIN LocalTalk and RS422 PinoutĒ diagram here would probably describe your connector

Apple Computer Bus, 8-Pin Mini-DIN Pinout and signal assignments

If you look at figure 2-16 on page 16 of your manual -

http://cdn-data.motu.com/manuals/mid..._Guide_Win.pdf

- it doesnít say you can connect two of the devices together, only that a Mac with a serial port can be connected to the NET port on your device. But I think you are saying the company told you that you can connect two of the devices together via the NET port if you use a NULL modem cable. Certainly sounds feasible but you wonder why that wasnít included in the manual.

It seems like the cable you made should have worked if a cross-over cable will work. But maybe pin 7 (General Purpose Input) is used somehow and that will be included in the cable you ordered.

Maybe thatís the wrong manual but it seems to imply that the USB interface (page 17) should be used to connect multiple MOTU devices (but I didnít give it a thorough reading).

(Brings back nightmares when we were building systems and would get some of our custom cross-over cables of all sorts mixed in with straight through cables and spent many joyful hours chasing problems of our own making, LOL)
 
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Old 06-11-16, 06:58 AM
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RS-232 is unbalanced, meaning that the TX and RX share a common signal-carrying ground. A "Null" serial cable will not be a pin-for-pin pass through; rather, it will have TX (transmit data) at one end connected to RX (receive data) at the other.

RS-422 is balanced, meaning that there are two signal wires for transmit (TX+ and TX-) and two for receive (RX+ and RX-). There is a ground, but it does not carry a signal. A "Null" cable in this case follows the same method as RS-232: TX at one end is connected to RX at the other. THe difference here is you have two TX and two RX. Proper polarity has to be observed, so TX+ would connect to RX+, and TX- to RX-. I read somewhere that there is no handshaking, so only those connections (plus ground) need to be made to the 8-pin DIN connectors.

Either drawing can be used for reference, but they are showing the female end. Since you'll be wiring the male ends, keep in mind that pins 1, 3, and 6 are on the left as you look at the open end of the connector.

Connect pin 3 at one end to pin 5 at the other. 4 to 4. 5 to 3. 6 to 8. And 8 to 6.
 
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Old 06-11-16, 02:56 PM
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@rick johnston so there really isn't a way to safely / effectively rewire a RS232 to be a RS422? seems like there were about 9-10 wires in the cable i have:

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even though the ends are identical.. what's connected behind them seems to be significantly different.. grounding.. shielding.. and more wires than pins.

I REALLY hope this next cable that arrives is just right.. it seems to say all the right things.. crossover.. localtalk..d
 
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Old 06-11-16, 03:24 PM
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keep in mind that pins 1, 3, and 6 are on the left as you look at the open end of the connector.
I think that is good advice. Iíve seen that type of confusion more than once Ė and maybe Iíve even screwed that up, LOL. (I confess, I did)

Looking at the manual again I just donít see how connecting another Midi Time Piece AV on the NET port will work. To me the manual sure seems to imply that they CANíT be networked together like that.
 
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Old 06-12-16, 02:43 AM
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it is definitely possible:

if you look on page 20 "NETWORKING TWO MIDI TIMEPIECES (For the MIDI Timepiece AV only)"

http://cdn-data.motu.com/manuals/mid..._Guide_Mac.pdf

through the "net" port.. you set the usb device to be 1-8 and the networked AV to be set to 9-16

"The two networked MIDI Timepieces then operate together as a single interface with 16 MIDI IN ports and 16 MIDI OUT ports"


as for the pin confusion.. yea i see how it can be, but is an RS-422 cable filled with less wires?

when i mapped it out.. looking at it with the two pins on top:

1 - red
2 - brown
3 - green
4 - yellow
5 - orange
6 - black
7 - blue
8 - grounding

however there was a gray and purple cable that appear to have no connection.. though in hindsight i realize i don't think i tested those cable at all since all eight pins were accounted for.. maybe some doubling up?
 
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Old 06-12-16, 06:11 AM
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If the raw cable was bought in bulk it could be used for DB-9 connectors as well. So it stands to reason that there would be extra unused conductors.

Depending on the year the thing was designed AppleTalk may have made use of pins 1 & 2 as well for handshaking. In addition to the above connections, connect 1 to 2 and 2 to 1.
 
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Old 06-12-16, 06:47 AM
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ugh.. crazy how that kind of stuff would change.. but apple's never been shy from making things obsolete to require upgrading.. that appletalk starter kit looked promising until i saw the pictures of the prongs and they were not just wrong but something i'd never seen before..

I can't wait to get that cable in the mail.. ugh.. been stuck on this issue for a week or two now..
 
  #20  
Old 06-12-16, 10:59 AM
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it is definitely possible...
Well you certainly are correct. The manual I linked to in post #13 must be an older version. It only has 156 pages as opposed to yours which has 182 – and the entire section concerning linking two MIDI’s via the network port (p20) doesn’t even exist in the old manual, and there are no dates and version numbers on the two versions of the manual. That’s unusual.

But I agree, I think you can assume that feature should be in your product. They reference on page 20 (your manual version) “a standard AppleTalk serial cable”. There really doesn’t appear to be “a standard AppleTalk serial cable”– unless I’m missing something (look at this for example APPLE/MACINTOSH CABLES).

They do say that cable would have been delivered with an older version of your product. So they may have had a part number for that cable at one time, but I assume it’s so old that they weren’t able to give you the part number. There could be some of those squirreled away somewhere. Someone always has ancient stuff for sale, it seems.

But some kind of cross-over would have to occur for two like devices to communicate. So a NULL modem cable would make sense. But all these standards leave it open as to which signals you choose to use. Hopefully that M1527 cable will work.

But ... maybe the Appletalk cable wouldn't be listed as one of the serial cables above, because it's ... well...an Appletalk cable, LOL - who knows!
 

Last edited by zoesdad; 06-12-16 at 11:17 AM.
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Old 06-12-16, 04:03 PM
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yea there was a pure-serial version before the usb version i must have linked that one by accident. it is hard to tell them apart.. literally the only difference seems to be the addition of a usb port.

no i agree there is no "standard" appletalk cable though you'd think there would be.. at least name them different! appletalk 2..

yea no cables came with mine.. these are 2nd hand recent purchases..

and yea unfortunately so far the MOTU folks haven't been helpful.. i mean exactly.. at least let me know what kind of cable they used.. or look up some schematic of what the wiring expectation was.

I think this network cable will be my last attempt.. as it is I have a Midi Time Piece AV and a midi express xt usb which effectively gives me the same 16x16.. but the XT would be worth more to sell than the non usb AV's (best kept secret for midi merging though)
 
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Old 06-13-16, 08:42 AM
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part12-

... at least let me know what kind of cable they used.. or look up some schematic of what the wiring expectation was.
I agree. They aren’t much help. They might now have no idea at all how some of the old stuff works themselves.

I think there may be something you could do which would be a little trouble, but I don’t think very expensive. You could use a mini RS232 patch box, some connectors and cable and via trial and error figure out what the correct wiring for a working cable between the two MIDI’s would be. You could then make your own cable according to the knowledge you had gained, or have one made up. Or I guess you could just let it run with the patch box and not even make up a new cable.

The patch box is just a simple device like this:

CA40 Rs232 Mini Patch Box, Connectors & Adaptors | Wagner Online Store

You would have to make 2 cables: mini Din 8-pin male connector on one end and DB25 male on the other end. I believe you can use crimp connectors and the connectors are cheap.

A cable would connect the MIDI to the patch box. You can then cross over signals and wrap back signals in the box and map them any way you want. I think you would find out which signal mapping from MIDI to MIDI worked.

I haven’t done any of this stuff myself for decades and I’ve forgotten a whole lot, LOL – but I’m pretty sure the above method would work. (I don’t think you would have to buy a crimping tool. I believe needle nose pliers work also, just slower. Maybe someone else who has made cables will weigh in.)

p.s. forgot to say you can always "buzz out" the cable, i.e., check out end-to-end using an Ohm meter for any pin-to-pin connectivity.
 

Last edited by zoesdad; 06-13-16 at 08:54 AM. Reason: added p.s.
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Old 06-13-16, 10:24 AM
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yea that's kinda what i'm thinking too about MOTU. They are not being coy it's just hard to say that the people there now are even the people who did the work back then.. 15+ years is a long time for one person to be at a company and 15 years ago.. the guys doing it were probably senior guys at the time with years already under their belt..

wow that's a fantastic idea.. I'm determined to figure this out now.. lol.. i hope that cable arrives today! i just want to know once and for all.. it just seems like MOTU didn't use a custom cable... they used something standard.. even if it were a specialty cable.. it was an apple product.. why else would they call it an appletalk cable? So yea I may try that suggestion if this next cable doesn't do the trick.

Also.. can anyone confirm if 232 / 422 cables send voltage? can i damage my equipment with a wrong wiring? my prior attempt made both units kinda light up but clearly in a way that's NOT right.. and that's fine.. so long as I'm not potentially doing damage to the devices!

it would be more comfortable knowing i can experiment without fear of actually ruining the hardware.. i mean technically i don't really know if i even hurt my units already with that attempt. I like to think it was just "signal" voltage which as i understand it is not dangerous levels.. but then again i ordered a modem that had a serial cable for apple (turned out to be hard wired into the modem) was powered by the serial port so clearly some voltage exists but maybe the modem didn't need for much power to operate.

Thanks!
Caleb
 
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Old 06-13-16, 12:23 PM
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I agree, itís got to be just one of the Apple standard cables. It drives you crazy, it seems like such a simple question but they canít help.

Iím not a hardware guy but I donít think you would do any harm to your equipment by routing signals through different paths from one NET port pin to another pin on the other NET port. I believe the RS422 line driver circuits (not software drivers) in the MIDI would put out the proper RS422 voltages (-6 to +6) on the lines and also protect themselves from excess voltages. They probably use standard chips for that as I canít believe they would reinvent the wheel and that stuff is built-in. I donít think there is any way by playing with the signal routing between NET ports you could hurt the MIDIís.

Maybe one of the more hardware oriented people would weigh in but Iím pretty certain thatís the case. But hopefully the cable you ordered will work and you donít have to worry about any of that.
 
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Old 06-13-16, 04:09 PM
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thanks for the unofficial reassurance.. i DO imagine it's safe though since this is a proprietary connection for the sake of transferring data.. not power. i see no reason why they would transfer power between two independently self-powered devices.
 
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Old 06-21-16, 05:15 AM
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after much experimentation and exploration I have found a cable that works!

Mini DIN Minidin 8 Pin Serial Crossover Cable Mac TX RX | eBay

the seller is kraydad in case this link becomes invalid / outdated. I ordered a 2nd one to have a spare.

Thanks for all your help folks.

Lastly if anyone reads this and happens to want to do a similar situation.. i hear that these USB units do not work with windows 8.1 / 64 bit (usb getting too old for newer windows)

on my G4 mac under OS9 / Digital Performer 3.. in freemidi configuration.. you turn them on after connecting the cable.. it should see the usb unit alone.. then under configuration.. you do a refresh / scan.. and the 1-8.. appears as 1-16.. as one solid device.. not two devices.

Thanks!
Caleb
 
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Old 06-21-16, 06:58 AM
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Wow! Thatís great to hear. Donít know how you did it. That cable even on their store home isnít even listed under ďMac Cables and SwitchesĒ but instead under ďMinidin 8-pin cablesĒ even though some of the Mac cables are Minidin 8-pin.

I like the fact that they tell you the exactly which pins are used and crossed. Handshake signals crossed and Data signals crossed, General Input and Ground straight through.

That was a good find. Glad to hear you are in business.

Good luck!
 
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Old 06-21-16, 09:01 AM
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yea quite journey but worth it.
 
 

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