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Dial Modifiers
Dial modifiers are characters than can be included in a phone number to make the modem
perform special tasks while dialling. For example, not all modem users will be using a dedicated
telephone line. Some users will have their modems connected to PABXs. To allow users of
PABXs to operate their modems successfully, dial modifiers are supported on the modem.
Most PABXs require you to dial 0 or 9 (in order to obtain an outside line) and wait for a dial
tone before dialling the actual phone number. Using dial modifiers, you can successfully dial the
phone number 12345 through a PABX using the command:
ATD0,12345
The , (comma) dial modifier causes the modem to pause for a short time after dialling 0. This
allows most PABXs sufficient time to obtain a line before dialling.
The factory default delay for the , modifier is two seconds. You may change the length of this
delay if necessary. Its length is determined by the value in S Register 8.
Another method of making the modem wait for a dial tone is to include the W dial modifier. The
W modifier causes the modem to examine the phone line to ensure a dial tone has been applied
before dialling starts:
ATD0W12345
If the modem cannot detect a dial tone within the time specified by S Register 7, the modem will
return to local command state and send a NO DIALTONE message to the computer (if either the
X2, X4, or X5 commands have been issued).
Due to differences with some older telephone exchanges, dial tone detection may not be possible
with your modem. Your modem will only recognise dial tones between 200 Hz and 600 Hz.
If your telephone line supports tone dialling then a useful dial modifier is the T modifier.
Inserting a T modifier before the number you are dialling causes the modem to tone dial that
number. For example:
ATDT12345
This will cause the modem to dial the phone number 12345.
These modifiers may be placed at any point in the number you are dialling and they may be
intermingled in the same number. More information about dial modifiers can be found in the
Command Descriptions chapter of this guide.