Modem and printer cable info for old Macs - Copyright Mar 20 2003 HRJ updated 5/30/05 
See my Mac modems section for the modems
I have available. See my printers page for
printers. All my Mac stuff is linked to from
my Mac home page. A Web link to my home page is at the end of this
document.

Modems

Modems are devices that connect your Mac to the Internet via phone lines.
I have some older modems that will be adequate for some of my Mac clients.
They are connected externally to your Mac at the modem port, you will need
a cable for these. While these are slower than the external 56K modems now
available, they are a lot cheaper! And for email and occasional Internet use,
they may be adequate. Also, older compact Macs like the Plus, SE and so on will
only support continuous speeds of 9600 or 19,200 baud anyway: a faster
modem will not provide faster Internet access.



For information on how to connect your Mac to networks or the Internet,
please look over my list of Mac Web site pointers to
find those Web sites which support these kinds of applications. I simply
cannot offer recommendations or tell you what you "should" buy, that
is a conflict of interest for me as a seller. These sites are not selling
anything, they are free to offer their advice and opinions.



The non-Apple modems use the Hayes compatible command set. Many
Mac telecommunications and Internet programs allow the use of these kinds
of modems. Consult your programs to see if these would be compatible. If I
have docs for these modems I will provide them. At these prices I can't
provide support or technical info; but they are tested for operation
by dialing out and running a terminal session. Most of them are low
flat boxes about the size of a paperback book, with a "wall wart"
power supply. A few are smaller.



Late model external modems from US Robotics are pretty common. The modem
has a set of switches that must be set for proper operation. The settings
that seem to work well are below, but your software's needs and modem may
vary.

        1 down (DTR override)
        2 up  (Verbal result codes)
        3 down (display results)
        4 up (echo offline commands)
        5 down (no auto answer)
        6 up (carrier detect normal)
        7 up (load NVRAM defaults)
        8 down (smart mode)

Most non-Apple modems will require a DB-25 to Mac DIN-8 modem cable. My
 Web page on
available modems offers these cables. Most of the modems made
for the IBM-PC market use a DB-25 connector. Most Macs use a DIN-8 connector;
(the very oldest 128K and 512K Macs use a DB-9). So you need a cable to
fit your Mac's modem connection to the DB-25 connector on the modem.
The way the cable is wired for use with a modem and its DB-25 connector,
to your Mac's DIN-8 connector, is as follows:

DB-25  2   3  4  5   7   20
DIN-8  5   3  2  1  4&6   2

all other pins are not connected.

Printers

The original Apple Apple Imagewriter I printer used a DB-25
connector, cabled to the Mac 128K, 512K computer with its DB-9 connector;
or to a DIN-8 on later Macs. Here's how an Apple cable, model 590-0555-A,
is wired between the DB-25 for the Imagewriter I, and the DIN-8 for
the Apple printer connection:

DB-25  2  3  6  7  8  20 
DIN-8  3  5  2 4&6 2   1

To use a MODEM-CONFIGURED DB-25 to DIN-8 cable for an Imagewriter I, 
you need to connect between the printer's DB-25 and the cable's DB-25,
a device called a null modem. This is a device that reverses 
some of the lines between the cable and the printer. If you compare
the modem cable's connections and the printer cable's connections,
you will see that some are reversed.

Computer to computer, or other devices

If you want to connect your Mac's serial port to another computer or to
some other device, you'd need to consider how their serial lines are connected.

In general, communications between serial devices (like
old printers and most modems) are divided between "transmit" signals
from the Mac, and "recieve" signals to the Mac. Sometimes those are
wired "backward" so a null modem rewires them "backward" again to
create the proper connections. This note is too short to detail
the signals on a Mac, a modem and on a printer. Consult documentation
and other sources for that information.

Herb Johnson
 my Mac Home page