Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 283)

AN93
Rev. 1.3 283
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.
Figure 64. Appearance of Bell 212 Protocol
Figure 65. Appearance of V.22 Protocol
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.
DTMF dialing
Bell 212 (2225 Hz
Answer Tone)
Unscrambled Binary
Scrambled Binary
Ones and Scrambled
Data; visually indis-
tinguishable from each
other.
Ones (USB1) signal.
Two tones at 2250 and
2850 Hz.
Calling modem’s
Scrambled Binary
Ones and Scrambled
Data; visually indis-
tinguishable from
each other.
DTMF dialing
2100 Hz
Answer Tone