Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 285)

AN93
Rev. 1.3 285
As shown in Figure 68, the V.29 FastPOS protocol looks different than the older, slower V.22-like protocols. It is
also half-duplex, and each participating modem uses the entire spectral space available on the telephone line.
A receiving modem recognizes that the calling modem is V.29-capable by detecting the V.29 calling tone at 980 Hz.
Another example with some more SDLC-oriented data is provided later in this document.
Figure 68. Appearance of V.29 FastPOS Protocol
DTMF dialing.
V.29 Calling
Tone (980 Hz).
Answer Tone
(2225 or 2100 Hz).
Answering modem
sends training pat-
terns and packet(s).
Calling modem sends
training patterns and
packet(s).
Modem exchange packets.