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3. OPERATION
3.1 Calling
An HSD call may be made automatically or manually.
3.1.1 Automatic HSD call
All automatic HSD calls are carried and terminated from the HSD terminal. Automatic
HSD calls begin when the DTE raises the DTR line in the serial connector. The Inmarsat
terminal dials the pre-programmed number. Upon answer by the called system the HSD
port is enabled and data transfer can take place.
Automatic HSD calls fall into two categories: direct call and address call. The category
may be selected with DIP switch SW1: turn off the switch (default setting) for direct call;
turn on the switch for address call. See page 3 for DIP switch setting.
Direct call setup
• Program subscriber number. See page 5.
• Turn off DIP switch SW1.
The subscriber is called when the HSD terminal turns on the DTR signal.
Address call setup
• See page 13 for sequence.
• Turn on DIP switch SW1.
The HSD terminal must support address calls. The HSD terminal outputs the following
command to the HSD modem in the format set by DIP switch SW4 and SW5:
CRN x x x x x (V.25bis command; x x x x x = subscriber number)
For further details about the CRN command, see page 10.
Note : If personal computer cannot call by user’s application having V.25 bis terminal
interface, call by DTR dailing (Direct call).
Clearing automatic HSD call
An automatic HSD call is cleared when the DTR signal is received from the HSD termi-
nal.
The HSD terminal turns off DTR, then the automatic call is cleared.
HSD terminal sends clear signal to CES, then the HSD modem turns off DCD and CTS.
Finally, the HSD modem turns off DSR.