Specifications

AN93
Rev. 0.9 199
Details of Some Low Speed Protocols
The following annotated recordings are shown to give very fundamental views of what to expect the EPOS modem
transactions to look like. There are many possible variations of these examples, both in compliance with the
specifications and not, but supported by common use. There are also very unusual variations that Silabs 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