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[makott]

Problems with mini din 8 serial ports and MIDI interfaces
Hi guys, I need help, information, and spiritual comfort :-)

I'm trying to set up a MIDI to DMX setup with old Macintosh computers and MIDI interfaces.

I have an 8100 Maxpower G3 System 9.1 that works perfectly, and I have a PowerBook G3 Wallstreet 300 System 9.2 that also works. OK.

I have an MIDI Opcode Studio 4 interface and a MIDI Motu MTP AV interface, fine. I've tried a thousand ways but it doesn't work! The interfaces are not recognized.

8100 >Studio4 with OMS 2.3.8/2.3.5 nothing.

8100> MOTU with Freemidi 1.44 nothing.

Same thing with Powerbook G3.

With a cable, different from the one used to connect the interfaces, which has a mini din plug on one end and eight exposed wires on the other, I made a loopback by connecting the wire from pin 3 and the wire from pin 5, as described in many tutorials. Okay.

Computer serial port test with "loopback cable" and TechTool Pro 3 “passed.”
However, if I try to run the test with the normal cable connected to the computer and the interface, the test fails. The cable is not an original serial cable, but it is well known and has been tested with a multimeter by a technician who assured me of pin-to-pin continuity.

Where could the problem be? Non-original Apple mini din 8 serial cables? (But sold as compatible pinout pin to pin)

Problems with "stack AppleTalk" occuped serial port comunication?

MOTU/Studio 4 settings?

All the serial ports on the interfaces are dead?

Help me!

Thanks for your attention.

EDIT: I read this post https://macos9lives.com/smforum/index.php?topic=7542.msg58406#msg58406
 while searching the forum. Could it be that the cables need to be crossed ? I'm confused now!

[GaryN]

Don't feel bad. This is simple but has tripped up countless numbers of users over the years.

Loopback is NOT the answer. You need - to be precise - an RS-422 Mini-DIN8 crossover cable.
Long ago, they were also referred to as "null modem" cables.

I have a diagram that I can't find…… big help huh? However:
This protocol and connection is used when two-way communication is required, such as between two computers or maybe a computer and a CPU-equipped MIDI interface LOL…

The point is that there are two transmit pins and two receive pins on each connector.
The Tx and Rx lines are "crossed over" so the Tx goes to Rx and vice-versa.
There's also a signaling line that's crossed over too.

The pin connections go this way:

1>2
2>1
3>5
4>4
5>3
6>8
7>7
8>6

More info HERE: https://macos9lives.com/smforum/index.php?topic=2656.msg15948#msg15948

You can actually buy these but you have to be certain the seller knows what they're selling because the industry, in its infinite wisdom, didn't think is was necessary to actually require marking these cables somehow to differentiate them from the straight-thru types. More than a few people have bought MINI-DIN cables for their Mac-whatevers and found out the hard way that the cables didn't work for them.

Here's one that's correct:
https://www.ebay.com/itm/232343545580