Sun Serial Cable Workaround

If you come across an old Sun machine, you can boot it without a monitor and keyboard by hooking up a “console” to the serial port. The console can be a PC comm program (like Miniterm on Linux). Set the terminal to 9600 baud 8N1 or 7E1.

Important Tip My mobo, an Abit BP6 (see Review: Abit BP6 Dual Celeron) has a problem if I’m connected to the internet on COM2’s modem and I try to boot the Sun on COM1. It just doesn’t work. The solution seems to be to get off of the Net, boot the Sun, and continue. I don’t know why this is, but that’s what works. (I sometimes managed to get it going by using Xon/Xoff instead of Hardware flow control, so it’s probably related to that.)

The only thing that’s hard to find is the serial cable. I made a mistake and got a mac serial printer cable (din 8 to 9 pin D), assuming that a printer cable is a serial cable. That’s not the case.

The correct cable is a hardware handshaking modem cable, with a null modem in between. The most common Mac modem cable is din 8 to male DB-25. You need a female 25 to female 9 null modem cable.

You can build your own null modem with a couple connectors and wires.

Here are the pins for the null modem (this one is for connecting the common 25 pin to the 9 pin serial port on your PC):

 9 pin    25 pin
 3 td      3 rd
 2 rd      2 td
 7 rts     5 cts
 8 cts     4 rts
 5 gnd     7 gnd

You should be able to find a 25-25 null modem, as well as a 9-9 null modem. The 25-9 null modem might be a little harder to find. 25-9 adapters are easy to find. The simplest solution with the longest term gain is to buy multi packs of D-type connectors (9 and 25 pins) and some crimp-on pins and holes. $20 will get you enough to build whatever you need (gender changers, null modems, loopback, etc.)

With these serial port issues, I often end up making my own stuff, because the packaged dealies often don’t work out or are really expensive. Serial ports are usually only five wires, so it’s so difficult to make cables.

I got the null modem information from:…

I also got other information from… and… and…

And, finally, I found another serial port resource:…