Multi-Tech ISIHI-2S Specifikace stáhnout pdf (Strana 150)

150 MultiModemISI Hybrid Series, ISIHI-2S/2U

Appendix

Appendix H: Dial Pulses and Tones

Dial Pulses

When you pulse dial, as when you make a call with a rotary dial telephone, your

telephone or modem generates codes in the form of pulses that simulate the opening and

closing of old-fashioned electric relays, or switches. The number of pulses in a code is the

same as the digit they encode; thus, the digit 1 is represented by one pulse, the digit 2 by

two pulses, etc. In the figure below, the digit 2 is pulse dialed, followed by the digit 1.

Each pulse consists of an A ms open (break) and a B ms closed (make), where A is either

60 or 67 ms, and B is either 40 or 33 ms, for a total of 100 ms per cycle, or a rate of 10

pulses per second. The interdigital pause time is 800 ms. The pulse ratios are controlled

by the &P command.

Closed

Open

Digit 2 Digit 1

Tone Dial Frequencies

The tone dialing method combines two frequencies for each of the twelve digits found on

a touch-tone dial pad. This method is referred to as dual-tone multifrequency (DTMF)

dialing.

The four horizontal rows on a touch-tone keypad use four low-frequency tones (697, 770,

852, 941 Hz), while the three vertical columns use three high-frequency tones (1209,

1336, 1477 Hz). The tone frequency tolerance is ± 0.02%.

For example, the digit 4 is dialed by combining two tone frequencies: 770 Hz from the

second row, and 1209 Hz from the first column. In another example, the digit 9 is dialed

with tone frequencies 852 Hz and 1477 Hz.

Hz Digits

697

770

852

941

Hz 1209 1336 1477

1 2 3

4 5 6

7 8 9

0 #

1 2 ... 145 146 147 148 149 150 151 152 153 154 155 ... 187 188

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Multi-Tech ISIHI-2S Specifikace Strana 150