Multi-Tech Systems MT3334HD8 manual Appendix B Dial Pulses and Tones, Tone Dial Frequencies

B Dial Pulses and Tones

Appendix B 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 are the same as the digit they encode; thus, the digit 1 is represented by one pulse, the digit 2 by two pulses, etc. In Figure B-1, 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

B

A

Digit 2 Digit 1

Figure B-1. Dial pulses

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 multi-frequency (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.

HzDigits

697

1

2

3

770

4

5

6

852

7

8

9

941

*

0

#

Hz 1209 1336 1477

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