The MacTerminal mini-HOWTO

2. Setting up a serial link.

To set up a serial link between a Mac and a Linux machine, you will need, on the Linux side, either a DB9 Female-to-DB25 Male serial cable or a DB25 Female-to-DB25 Male serial cable, depending on your serial port. On the Macintosh side, you will need a DIN9-to-DB25 Male high-speed modem cable.

Make sure that the cable is labeled a "high speed" cable, because some older Macintosh cables are configured with their handshaking lines tied high, which makes them useless for high-speed serial connections.

You will also need a null modem adapter, available at Comp USA, Radio Shack, and similar outlets, and a DB25 Female-to-DB25 Female serial gender changer to connect the two serial cables.

I have heard that Mac printer cables are really null modem cables in disguise, but I can't confirm this. Some of them are DIN9-to-DIN9 anyway, and wiring one into a serial link would be more trouble than it's worth.

If this sounds like Greek to you, read the Serial-HOWTO for details of RS-232 cable configurations and data transmission protocols.

Before connecting the Mac and the Linux machines, you should determine that you have a working serial port on both machines, either by connecting a modem and dialing out to another computer with minicom (Linux), ZTerm (Mac), kermit (either), or the communications program of your choice.

The latest version of minicom is available from sunsite.unc.edu/pub/Linux/apps/serialcomm/dialout and mirror sites.

ZTerm is a complete, easy to use comm program. Unfortunately, it's shareware. A current version is available from mac.archive.umich.edu and outlets like it.

The kermit program has been ported to every computer and operating system in existence. The archives are located at ftp.columbia.edu/kermit.

You should strongly consider using kermit on both machines at this stage at least, because 1) it's free (although it's not covered by the Free Software Foundation's General Public License); and 2) it's a lot less confusing to have kermit on both machines than two completely different communications programs.

If you have another way to determine that the serial ports of the two machines are operational, feel free to use that. The point is to ensure that both machines have working serial ports.

Making the actual serial connection should be easy, given the directions above. In case it isn't, the connection looks like this:

 Linux PC    DB9- or DB25-  Null     Gender   DIN9-to-       MacBox
 ---------   to-DB25 male   Modem    Changer  DB25 Mac      --------
 |       |   serial cable. |     |  |     |   Serial Cable  |      |
 |       |-----------------|     |--|     |-----------------|      |
 |       |                 |     |  |     |                 |      |
 ---------                  Adapter                         --------