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Chapter 5 - Command Mode
Result Codes (Basic and Extended) and Call Progress Selection X
The X Command is used to select one of two possible dialing methods (“dumb” or “smart”), and to
select various response combinations related to these methods. You can choose to have certain
responses suppressed, or whether or not you want speed indications along with the CONNECT
responses. You can also pick and choose certain responses in order to match up with “Standard AT”
responses. (Refer to Appendix G for a summary of Result Codes.)
The modem provides “Basic” and “Extended” Result Code sets. The difference between the two is
the Basic set provides one response (CONNECT) to indicate a connection, while the Extended set
provides several responses for different speeds (CONNECT, CONNECT 2400, CONNECT 4800,
CONNECT 9600, Etc.).
When the Extended set is chosen, you also have the option of matching them up with Standard AT
2400 response code sets, by including or not including the BUSY and/or NO DIAL TONE
responses while excluding the DIAL TONE response. The X command is used to select which
responses are provided.
Regarding the modem’s method of dialing, the modem can detect standard dial tones and busy
signals. This capability (“smart dialing”) allows the modem to wait for a dial tone, and when one is
detected, to begin dialing immediately.
The modem also can detect a distant busy signal, if after dialing, it reaches a busy number. This is
useful because it allows the modem to immediately abandon a call, rather than wait 45 seconds for a
carrier signal that will never come. S-Register S7 defines the wait for carrier time (refer to Chapter 6).
The modem gives you a choice between the wait-for-dial-tone (“smart”) method we just described,
and blind (“dumb”) dialing, where instead of detecting actual dial tones, the modem relies on timed
pauses. When the wait-for-dial-tone method is chosen, the busy signal detection capability is also
activated. The X command is also used to select which dialing method is used.
Five different X commands are available (X0 through X4), with five different effects on the modem’s
Result Codes.
X0 Provides the basic (short) result codes and provides “dumb” dial capabilities.
X1 Provides the extended result codes and provides “dumb” dial capabilities.
The remaining X commands affect Call Progress, and turn on Extended Result Codes.
X2 Looks for dial tone only and will not provide a busy response.
X3 Looks for busy only and not look for dial tone.
X4 Looks for dial tone and for busy.
The factory default setting is X0, which selects Basic Result Codes and the blind (“dumb”) method of
dialing.