D/I Mux III User’s Manual Appendix G. Modem Interfaces
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The basic sequence for modem call processing is listed below. More specific steps are listed in the
following section for connecting and terminating modems when using the D/I Mux III system, the Digital
Cross Connect II (DXC II) system, and the Network Communications Controller (NCC) system.
1. Acquire and initialize the serial port.
2. For each device in the connect path, initialize and connect the device.
3. Exchange data with the remote unit.
4. For each device in the connect path, disconnect the device (in reverse order).
5. Release the serial port.
Note: In all cases it is the responsibility of the calling unit, or node, to properly disconnect the call.
Modems and the NCC System
When the NCC program attempts to make or break a connection the activity sequence includes
making connection, processing messages, and terminating the connection. This is the case for
all versions of the NCC software product family.
Making Connection
Each of the components involved in the data transfer must be connected. The sequence of those
connections are listed below.
Port
Coastcom’s NCC5 program will first request the serial port from the system. If the port is
not available within several seconds, the connection attempt will be aborted. The NCC5
program will then initialize the port to the configuration in the program.
The NCC2 and NCC6 programs will save the original serial interrupt vector, and install
their own interrupt routines. These programs will then initialize the port to the
configuration in the program.
Modem
If a modem has been configured into the network follow the steps below, otherwise
proceed to the next section.
1. To ensure that the modem is not in an off-hook state, hang up the modem using the
following recommended hang-up string: ~~~+++~~~ATH0!
2. Wait 2-3 seconds.
3. Send the escape sequence: +++
4. Wait for an OK response (which should appear within 3 seconds), and continue as
follows.
5. Send the hang-up command: ATH!
6. Wait for an OK response (which should appear within 3 seconds), and continue.
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