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Developing Modem Applications
80-99208-1 Rev. D 5-9
• Control port only — only AT commands can be sent to
modem (no data).
• Data and Control ports — the DTE can receive data on
the Data port and, at the same time, communicate with
the modem on the Control port using AT commands.
The different Data and Control port configurations above are
based on which ports are defined as active:
• A port is active if DTR is asserted on that port.
• A port is inactive if DTR is de-asserted on that port.
Using both the Data and Control ports allows more
sophisticated communication with the modem and thus
better control of it, but requires that you understand the
modem’s port arbitration behavior.
Note
In this context, port configuration refers to which ports on the GSP-1620
modem are active, rather than to port baud rate, parity, etc.
Port Arbitration Behavior
This section describes the modem port arbitration behavior
for each of the following port configurations:
• Data port active only
• Control port active only
• Both Data and Control ports active
When a port configuration change occurs due to a DTR
change, the AT command configuration parameters
maintained by the AT command processor are not modified or
reset to their default values. The parameters’ current state
will be associated with the newly activated port when the
change occurs. An AT command in progress when DTR
changes will be silently aborted.
Table 5-3 summarizes modem port arbitration behavior.