Important Fact #2
On LINX terminals only the COM port has the correct hardware lines to support a modem. The
AUX port does not. Therefore, only attempt to use a modem on the COM port.
Setting up the LINX terminal, requires more work.
• Using the regular serial connection, load the “modem aware” application into
the terminal.
• Connect the modem to the COM port on the terminal.
• Set the Answer/Originate switch on the modem to Answer.
• Set any dipswitches that may be required. For the MT2834BL the switches
should be set as:
“UP, UP, DN, UP, UP, UP, DN, DN, DN, UP, UP, DN, DN, DN, UP, DN”
This differs from the PC modem only by switch 5 (the auto-answer switch).
• Use the configuration menus on the terminal to use the correct serial
communication settings for the modem. Again the defaults are 9600 baud,
EVEN/7 for parity/data bits, and 1 stop bit.
• Wait for incoming connections from Topsail.
The critical part here is making the terminal application modem aware. For this we hope
to show by example. Included below is a sample program that shows the code that needs
to be present for modem awareness.
In particular, note the following:
• We only attempt to issue the modem initialization string when the computer is
not ONLINE (i.e. communicating with the server), to do so would likely
interrupt a good connection.
• Initially we feed the modem an initialization string, assuming that it isn’t online
already, of course.
• Within the main execution loop, we continually check to see if the modem
becomes unavailable by checking the CD (Carrier Detect) line status. If this line
drops to low and then becomes high again, the modem has been disconnected
(or power interruption, etc) and the modem needs to be re-initialized.
Sample Code
' SIMPLE SAMPLE UTILIZING MODEM FOR COMMUNICATIONS
'
' Please note terminal applications wishing to utilize
' a dial up connection should employ similar techniques
' to insure proper initialization of the modem.
'
' You must have the following OS or later for the
' techniques discussed here to work.
'
' LINX III OS (v)10.3 and greater
' LINX IV OS (v) 3.4 And greater
' LINX V OS (v) 3.9 And greater
' LINX V A OS (v) 10.2 And greater
'
CONST FALSE=0
CONST TRUE=-1
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