
Click above to get retro games delivered to your door ever month!
X-Hacker.org- Telix/SALT v3.15 & RS-232, Hayes - Norton Guide
[<<Previous Entry] [^^Up^^] [Next Entry>>] [Menu] [About The Guide]
CABLES TO CONNECT A COMPUTER TO A MODEM
A normal modem cable runs straight through with pin 1 to pin 1,
pin 2 to pin 2 etc. The end that hooks onto the terminal
presents a female connector to the terminal's male, and the end
that hooks onto the modem presents a male end to the modem's
female.
Sometimes the sex of connectors can get confused and you will
need non standard sexed ends on your cable.
Nearly always one end of the connection will support a different
subset of the pins from the other. For example, the modem may
be watching RTS but the terminal doesn't support it. In that
case you have to fake it by strapping the RTS pin permanently ON
by connecting it to the +12V test pin, or by strapping it to
some other signal such as DTR that the terminal does support.
The pins you have trouble with most often are 4, 5, 8, and 20
(on a 25 pin connector).
You can find out which lines are being supported by perusing
documentation or by using a $200 breakout box. A breakout box
is a set of 25 LEDs. Fancy versions use Red/Green/Yellow to
indicate line state. They also come with a set of switches and
little jumper wires so that you can build experimental cables
instantly. One of these days when I am rich I am going to get
one. You can also see if signals are in spec. Sometimes the
signals that are nominally +5 volts droop down in the 2.5 volt
range, which is no-man's land. Ordinary LED tests will not show
up the trouble. Once you find the magic combination you can get
a permanent cable built for about $30.
See Also: connectors 25 to 9 pin correspondence
Online resources provided by: http://www.X-Hacker.org --- NG 2 HTML conversion by Dave Pearson