Multi-Tech Systems ISIHP-4U, ISIHP-4SD manual Dn Data Terminal Ready Control

Modem AT Commands & S-Registers

Default: &C1

Allows you to control the Carrier Detect (CD) signal on the RS-232/V.24 interface. This is a signal from the modem to your computer indicating that the carrier signal is being received from a remote modem. Normally, CD goes high (turns on) when the modem detects a carrier on the communications link and drops (turns off) when it loses the carrier. By using &C, you can force the signal to stay high, or to drop momentarily when the remote modem disconnects. This option is useful with some CBX phone systems and mainframe front ends, which require CD to act in this manner.)

&C0 ignores the state of the carrier from the remote modem. CD is forced high.

&C1 allows CD to act normally—to go high when the modem detects a carrier, and to drop when it loses the carrier.

&Dn Data Terminal Ready Control

n = 0, 1, 2, or 3 Default: &D2

The Data Terminal Ready (DTR) signal on pin 20 of the RS-232/V.24 interface must be high, or on, in order for the modem to operate. A high DTR signal tells the modem that the computer it is connected to is ready to communicate through the modem.

The DTR signal can also be used to cause the modem to reset to its default parameters, as if you had given the modem an ATZ command.

&D0 (or &D) causes the modem to ignore the DTR signal and treat it as always on.

&D1 causes the modem, if in online data mode, to enter command mode, issue an OK and remain connected when the DTR drops.

&D2 causes the modem to hang up when DTR drops while the modem is in online data mode.

&D3 causes the modem to reset when DTR drops . It will also hang up if it is online.

MultiModemISI Hybrid Series, ISIHP-2S/2U/4S/4U/4SD 87