Setup
Software should provide some modem setup. The software can be written
to retrieve modem configuration from a stored profile recalled on reset,
or by DIP switches set for the product. Unique settings must be set up prior
to running the software, before the program sends a Zn
- Perform Soft Reset command to recall a stored profile. Software assumes
the modem is in the power-up state. Unless the software is used in a predictable
environment, these assumptions may result in failures with the controller
software.
Some commands are always overridden by the controller to ensure proper functioning.
Other command options should either default to the factory setting, or act
as the transfer agent for the commands. You can provide menus and dialogs
to prompt the user for specific activities; the program can then interpret
these requests and configure the modem accordingly. The program should also
allow the user to enter AT command strings.
Commands frequently set by a modem controller include:
E0 Turns off echo mode to avoid having command echoes pass through
the result code scanner.
&F Recalls the factory profile.
Q1 Enables result codes to ensure that commands are being processed,
and to synchronize with the modem command processor (except for
synchronous communications where result codes may cause the DTE
confusion).
V0 or V1 Uses either numeric result codes or verbose (recommended) result
codes.
S0=0 Disables auto-answer in setup process to avoid disruption by
incoming calls.
H0 Ensures modem is on hook before continuing to the answer or
originate process.
S12=10 Sets the escape sequence guard time to 200 ms to speed up the
escape for hang-up process. This also reduces the probability of
inadvertent user escapes.
S2=* Changes the escape sequence character for two reasons: To avoid
inadvertent user escapes, and to provide different escape sequence
characters for answer and originate ends. This prevents inadvertent
escaping when data is echoed.
S4=* Modifies the linefeed character to make the <CR><LF>NO
CARRIER<CR><LF>result code unique if you scan for it to
detect carrier loss.
S95=60 Enables the result codes which provide the maximum amount of
information about the connection when it is established.
Two typical setup sequences using these recommendations follow:
Software design based on using pre-existing user settings:
AT E Q V S0=0 H S12=10 S2=28 S4=31 S95=60 <CR>
Software design based on starting from a known factory setting:
AT &F S2=28 S4=31 S12=10 S95=60
Note: Where the zero suffix is used, it may be omitted from a command.
Spaces are shown above for readability, but using spaces between commands
is not recommended.
After sending the setup command, and receiving the OK response, the controller
continues to originate or answer processing.
If additional setup strings include user-programmed settings or the user
is permitted to enter AT setup strings, the software should anticipate ERROR
result codes. If an ERROR is returned for a command, the result does not
have to be reported to the user, but the controller should not be prevented
from continuing. A connection can be made even though some setting is in
error or is inappropriate for the class of modem being addressed.
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