Guardian Technologies DVST 7.5Connecting a modem in direct mode, Call request, Call disconnect

Modems DVST Installation Guide

7.5Connecting a modem in direct mode

This mode uses a modem in a ‘dumb’ mode, and purely relies on the hardware control lines. Telephone number selection, and all other configuration must be performed at the modem.

The modem is controlled using DTR (Data Terminal Ready), and indicates it’s status using DCD (Data Carrier Detect).

Note: This mode is not recommended, easier operation is achieved in ATMODE.

Call request

A call is requested by making DTR active (high). At this point the MODEM dials it’s stored number, and attempts to establish the call with the remote end. 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, the modem answers the call, establishes the physical link, and then raises DCD to inform the DVST unit that a call is present. The DVST unit responds to this by taking DTR active (high).

Call disconnect.

This is requested by dropping the DTR signal. A successful disconnect is confirmed by the DCD line being dropped by the MODEM. In this mode the DTR line remains low.

Configuration of modem in direct mode

No configuration can be performed by the system, however the following are required of the modem :

Select synchronous operation.

Dial stored number on low to high transition of DTR.

Disconnect on a high to low transition of DTR.

DCD must follow remote carrier.

Ignore DTR to answer.

Auto-answer. ( If required ).

No flow control enabled.

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