Making an MMJ to DE25-F adapter

Tony, Thank you for your detailed description of how to make a cable. Unfortunately, my MMJ to DB25 adapter is made in such a way that I can't see inside to tell which wires go to which pins. All I can do is assume that the wire colors are the "standard" colors, i.e. green/red in the center, black/yellow one pair out, etc. While doing more research I also realized that I'm going to have to connect multiple wires to the same pins. The wires that come out of the MMJ jack have the "pins" right on them and they just fit into the holes on the DB25 connector. So, hooking up multiple signals to the same pin would be tough (I don't do soldering irons). I found a source to sell me an adapter to do exactly what I need (this adapter is what I thought I was getting in the first place, I didn't realize I was getting a "make it yourself kit"). So I figured I might as well order it and save myself a lot o f headaches. It should be here tomorrow. - Bob -----Original Message----- From: cctalk-admin(a)classiccmp.org [mailto:cctalk-admin@classiccmp.org] On Behalf Of Tony Duell Sent: Wednesday, May 29, 2002 6:47 PM To: cctalk(a)classiccmp.org Subject: Re: Making an MMJ to DE25-F adapter Argh!. I've spent years correcting 'DB9' to 'DE9', and now we get DE25 connectors ;-) There is no such thing. You are not going to pack 25 pins into the E shell (DE9 and (H)DE15 are the 2 that exist). For once you mean DB -- the standard RS232 connector is a DB25 (which is, I guess why the PC-crowd call all D connectors 'DB'). Anyway. I'll assume you mean DB. Well, the first thing we have to know is the wiring of that DE9 to DB25 PC cable. I think it's safe to assume that the DB25 is somewhat close to RS232, but is the cable a null-modem or not. With those connectors it should be (it would be used to connect 2 DTEs, both with male connectors), but I'd not bet on it. And I can't beleive the colour code is necessarily standardised. Here's what I would do. Start by looking at how the wires are connected to the existing DB25-F in the MMJ adapter. If we assume that's standard RS232 as well (again it could be either DTE or DCE), then we can do a couple of quick tests. Firstly, what pins are used on the existing adapter (and on the PC cable if you can check it). I would be suprised if pins other than 2-8 and 20 were wired. Then get one of those RS232 'quick checkers'. Tandy (Radio Shack) used to sell them. It's an in-line adapter with a DB25M at one end and a DB25F at the other. On the top are 7 bicolour LEDs. It passes all 25 pins straight through and also monitors 7 of them : 2 (TxD), 3 (RxD), 4 (RTS), 5 (CTS), 6 (DSR) 8 (CD) and 20 (DTR). Last time I bought one it cost about \pounds 10 I think. Not too expensive, and I use mine a lot. Conenct that to the existing MMJ adaptor (connected to a VAX or whatever). See which LEDs light up. Those are the outputs. Wires that are connected, but which don't light the LED are inputs Do the same with the PC cable. We can now make a guess at how to connect it (at least for starters). Pin 7 -- signal ground -- stays as it is. Move all the wires from that pin on the DB25F on the MMJ adapter to pin 7 on the DB25-M Pins 2 and 3 (the data lines). You need to connect an output to an input. So if pin 2 is an output on both the existing MMJ adapter and on the PC cable, you need to swap over these 2 wires. Ditto if pin 3 is an output on both existing devices. But if pin 2 is an output on one device and pin 3 is an output on the other, just keep those wires on the same numbered pins when you move them to the DB25-M Pins 4 and 5 (RTS and CTS), do the same thing with. Keep them as a pair, but link an output to an input Pins 6 and 20 (DSR and DTR), again, do the same with those. Of course you might have some weird combination of handshake pins used, but if you tell us which pins are currently wired on the MMJ adapter, and whether they test as inputs or outputs, we might be able to make a sensible guess. Looking at the wiring side of the DB25M (so also the face of the DB25F) 1 o o 14 2 o o 15 3 o .... 12 o o 25 13 o -tony