SERVSWITCH™
44
CAUTION!
Serial cabling in excess of 50 feet (15.2 m) should be routed with
caution. The maximum cable length depends upon the construction of
the cable and its routing. For extended runs, shielded cable should be
used. Avoid routing near fluorescent lights, air-conditioning
compressors, or machines that may create electrical noise. If you
experience a lot of data errors, use shorter cables. The ServSwitch’s
lowest data rate is 9600 bps; it cannot be lowered any further to alleviate
this problem.
4.4.2 Switching ports remotely (Optional)
To switch ports on a ServSwitch from a remote computer or terminal attached to
the Switch’s RS-232 port, take these steps:
1. Set your computer for serial communication at 9600 bps, no parity, 8 data
bits, and 1 stop bit.
2. To switch the ServSwitch to a different port, use a terminal-emulation
program and type or send the desired port number followed by [Enter]
(a
return).
NOTES
If you type or send a “?” (question mark) rather than a port number, the
single or master Serv unit will send the number of the currently selected
port
minus one
back to the remote computer or terminal—
as an 8-bit
binary byte.
For example, if you currently have port 1 selected, the
Switch will respond to “?” with the byte “00000000” (binary zero); if you
have port 3 selected, the Switch will respond with “00000010” (binary
two); and so on. You
must
be at some kind of prompt or screen capable
of displaying serially received text characters in order to see the
Switch’s response.
Of course, because most terminal emulators and similar programs
will interpret these values as ASCII codes, they will try to display the
corresponding ASCII characters instead of decimal numbers; and
because binary zero through binary thirty-one are control codes in
ASCII, if you’re running the terminal emulator on an IBM PC you will
probably see the port numbers displayed as odd text-graphics
characters (smiley faces, hearts, etc.) that remain in the PC’s custom
character set as relics of the graphics-poor days when the PC was
invented. You will probably need an IBM PC ASCII-to-decimal translation
table to visually identify which port numbers these displayed characters
stand for.
