AN93

Details of Some Low-Speed Protocols

The following annotated recordings give basic ideas of what to expect the EPOS modem transactions will look like. There are many possible variations of these examples, both in and out of compliance with published standards, in common use. There are also very unusual variations that Silicon Labs has made efforts to support in order to allow customers to connect to non-standard and essentially broken modems. Some of these are described in a later section.

Bell 212 (2225 Hz Answer Tone)

DTMF dialing

Answering modem’s Scambled Binary Ones and Scrambled Data; visually indis-

tinguishable from each other.

Calling modem’s Scrambled Binary

Ones and Scrambled Data; visually indis- tinguishable from each other.

Figure 64. Appearance of Bell 212 Protocol

2100 Hz

Answer Tone

DTMF dialing

Unscrambled Binary Ones (USB1) signal.

Two tones at 2250 and 2850 Hz.

Scrambled Binary Ones and Scrambled Data; visually indis- tinguishable from each other.

Calling modem’s Scrambled Binary Ones and Scrambled Data; visually indis- tinguishable from each other.

Figure 65. Appearance of V.22 Protocol

Rev. 1.3

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Silicon Laboratories SI2494/39, SI2493/57/34/15/04 Details of Some Low-Speed Protocols, Appearance of Bell 212 Protocol