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7.6 Using a modem in ATMODE

In this mode the Hayes set of commands is used, all of which begin with the letters AT.

Both call setup and configuration are performed using these commands.

The commands can be configured on the DVST unit in setup mode.

The modem is also controlled using DTR (Data Terminal Ready), and indicates it’s

status using DCD (Data Carrier Detect).

Call request

The DTR is normally active, unless the modem channel is turned off, or the unit is in

setup mode.

To dial a call the system sends the dial string (set by DIAL= in the DVST setup menu ) to

the modem, followed by the number selected.

For synchronous operation the modem switches to synchronous mode on connection.

When the call connect has been completed the modem raises it’s DCD line, confirming it

is connected with the remote location. A call already being active is indicated by the

DCD line being active (high) from the modem.

Call answer request

If a call is incoming, and the DTR line is high, the modem answers the call, establishes

the physical link, and then raises DCD to inform the DVST unit that a call is present.

Call disconnect

This is requested by a high to low transition on DTR. A successful

disconnect is confirmed by the DCD line being dropped by the modem.

In this mode the DTR returns high after a short delay.

7.7 General settings for modems in ATMODE

The modem is configured from the DVST unit using the following strings:

MINIT=general modem configuration.

SREG=typically used for setting of s-registers.

USER=optional string, typically for individual customisation.

DIAL=string used to dial, typically ATDT for tone dialling.

The configuration details stored in MINIT, SREG & USER are sent on power-up, leaving

setup mode, and on disconnecting a call. If a MODEM is not present a large delay will be

experienced while the system waits for replies from the MODEM. To avoid this the

command MODEM=OFF should be selected from the DVST setup menu. It is also

possible to transmit or send these values to the MODEM using the SEND command in

setup.

It is also possible to communicate with the modem directly using the MODEM

command.

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Guardian Technologies , LLC Home Security System DVST User Manual Page 35