Serial Switch Woes

[LaPorta]

Hi everyone,

I’m trying to use a serial switch I’ve had for years to switch an ImageWriter II between two of my machines. It hasn’t been used for over 20 years when I used to use it to switch between a printer and AppleTalk network (why, you may ask? Because of the “you don’t need a modem port with an internal modem” scandal of the Performance 6xxx series.”) Anyway...

Now, the Mac SE I have it connected to won’t print to the IW II. I hooked cables to the box that I’m using, and buzzed out each pin for continuity, including the shield for ground, and they all have continuity with no short between them. This is the common port to port A I buzzed out. It’s a dumb 4-port switch, manual terminals, no software or power. A serial cable straight from the SE to the IW II works fine. What am I missing here?

 

[Trash80toHP_Mini]

My guess it's a cable mismatch. Serial cable won't work for printing to the IWII, so if it does, you've got a null modem cable/printer cable there. If you've another like cable inline on the other end of the serial port switch box they'll cancel each other out to straight thru, no? That won't print and could be the reason you have pin to pin continuity between the two cables on either side of the switch, which you don't want. one side has to be crossover and the cable opposite needs to be straight thru. I used switchboxes all the time back in the day, had to mark every cable with an S or a P to keep things straight, or crossed over, whichever was needed.

 

[LaPorta]

So let me get this straight (since I am not very familiar with this). The printer cable reverses the pins so that they match up on the other side (mirror image). I'm basically flipping it by using two of the same cable. I wonder how in the world I ever made this work when I was a kid, just by blind chance? Where would one get straight serial cable then to make sure that there was reversal?

 

[mdeverhart]

I’m pretty sure (but not positive) that modem serial cables are straight through, while the printer cables have the cross-over.

If you put a straight through cable between the switch and the box you can use normal printer cables to go between each of the Macs and the switch. (I’m assuming you have printer cables, so this way you’d only need to find one straight through cable).

 

[LaPorta]

Thanks to everyone’s input, I did the easiest thing that I could since I only have 6 different cables that are all printer cables: modified the box to cross over the appropriate pins, so now the logic makes sense crossing, crossing back, then crossing again.

Thank you!

 

[Trash80toHP_Mini]

De nada, glad to see you've got it working well enough. Nice bodge. :approve: