Don't make this any more difficult than it is.
You need a straight cable with a 9-25 converter block.
DYNAPATH made it easy by inverting 2 and 3 on the 25 pin connector for you...HOWEVER, keep in mind that at the time the 9 pin connector didn't exist, and on the 9 pin connector 2 and 3 are already inverted...when compared to the 25 pin standard....
SO....if you are going from 9 pin on your computer to the 25 on the dynapath, you need a cable that is 2-3, 3-2 and 5-7 (5 on 9 pin is 7 on 25)....which might be tough to find..just wait....
NOW, you need to deal with the communications protocols.
Every RS-232 device has a 'buffer' that allows it to handle a few extra characters more than it needs / can handle for those times when the data is coming in faster than the computer can handle it.
Think of this as a bucket with a hole in the bottom. If you pour water in FASTER than it can run out the bottom, you have to have a way to tell the 'SENDING' computer to stop.
This STOP command can come in 2 forms...
SOFTWARE or HARDWARE
In hardware, you set certain voltages on pins to 0 or 5 volts to allow the data to SEND or STOP. This requires
RTS - request to send
CTS - clear to send
voltages go up and down as the 'bucket' gets full.
In software, you actually send a special character BACK to the sending computer (through the 2-3 cable) to say STOP until I send a GO character. This is often referred to as XON / XOFF or other schemes like (Xmodem, Ymodem, KERMIT - YES KERMIT and a few others). I am pretty sure that Dynapath only supports XON / XOFF....need to look in the manual to be sure.
OK, now for the good news.
If you are dealing with small programs and are not feeding a huge surfacing file to the control so that it is cutting the program as you are feeding it, you can pretty much forget about all this crap as long as you set the BAUD (data transmission rate) low enough....this is because the bucket will never get FULL and the control will never have to say STOP SENDING.
If I remember correctly, with the Dynapath, this is around 4800 baud, so if you send at 2400 baud all you have to do is pry the dynapath's mouth open, at which point it will patiently wait until the data starts.
As you feed the data at 2400 baud, it will store it faster than you are feeding it, so it just keeps swallowing the data as you send it. For small programs the 2400 Baud rate is no biggie...so it takes 20 seconds to send a program rather than 10 seconds...whoopee....
When you are done, your software sends an ASCII character meaning EOF (end of file) and the dynapath closes its mouth and the program is loaded.
I know it all sounds complicated, but it is quite easy, and I have communications software that I have written that runs in Windows if you want a copy..quite brain-dead to use (I wrote it, remember - so it must be simple from the source)....
Since you say you are going 9 computer to 25 dynapath, you need a cable that is straight through (9-9) and a 9-25 pin conversion block...NOT A NULL MODEM BLOCK....just get the straight through 9-25 converter, of the appropriate gender on each end....and it will be correct...leave the converter block in place on the control and connect the cable as needed. DO NOT LEAVE THE CABLE CONNECTED AT ALL TIMES. If you have a nearby lightning strike, you can kiss the RS232 chip in the control (or computer which is cheap) goodbye....
OH, and for those of you that are interested, RS-232 defines only signal form (voltages and timing), but does not restrict cabling or protocols used to control the data...which is why there are so many flavors of it.
Contact me off-line if you need more information and don't want to bore everyone else...especially if you want the software.