Multi-Tech Systems ISIHP-4S Cn Dummy Command CnData Calling Tone, Dummy command Gn Guard Tones

Modem AT Commands & S-Registers

initiating the handshake between the two modems.) At higher speeds

(2400 bps and above) there is no conflict because all protocols use the Bell frequency of 2225 Hz. Lower speeds require different frequencies.

B0 selects ITU-T V.22 mode when the modem is at 1200 bps.

B1 selects Bell 212A when the modem is at 1200 bps. This is a default. B15 selects V.21 when the modem is at 300 bps.

B16 selects Bell 103J when the modem is at 300 bps. This is a default.

Cn Dummy Command

-CnData Calling Tone

n = 0 or 1 Default: -C0

The data calling tone is a tone of a certain frequency and cadence, as specified in the V.25 standards, which identifies whether it is remote data, fax, or voice. The frequency is 1300 Hz, with a cadence of .5 s on and 2 s off.

-C0disables the V.25 data calling tone. -C1enables the V.25 data calling tone.

FDummy command

&Gn Guard Tones

n = 0, 1, or 2

Default: &G0 (models outside U.K.) or &G2 (U.K. models only)

Controls the presence or absence of guard tones from the transmitter when in answer mode at either 1200 or 2400 bps. Guard tones are used in Europe and other areas to allow the modem to function in the telephone systems.

Guard tones are not used in the United States. U.K. models are locked at &G2 (1800 Hz guard tone).

&G0 disables ITU-T guard tones. &G1 enables ITU-T 550 Hz guard tone. &G2 enables ITU-T 1800 Hz guard tone.

MultiModemISI Hybrid Series, ISIHP-2S/2U/4S/4U/4SD 85