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V.25 bis Command Set Operation
To return to V.25 bis command set mode, use the AT%Vn command.
To invoke this command, type:
PRS AT <LF>
PRS CM
Connect Message Inhibit
PRS CM controls the CNX yy connect message responses. The V. 34 supports both the 1989 and
the 1984 recommendations for V.25 bis connection procedures. The 1989 CCITT Blue Book
recommends that when the modem transfers from command mode to data mode it should send a
connect message of the form CNX yy, where yy identifies the connect speed (96 = 9600 bps, 48 =
4800 bps, 24 = 2400 bps, and 12 = 1200 bps; omitted for 300 bps). The 1984 CCITT Red Book
does not include these connect messages. Default is 0 (connect message disabled).
To disable the CNX yy connect message responses, type:
PRS CM ; 0 <LF>
To enable responses, type:
PRS CM ; 1 <LF>
Note
After modifying this option you should save the setting by using the NVW command.
PRS DR
DTE Data Rate
PRS DR, in conjunction with the handshake mode command (PRS HM), controls the DTE speed.
There are several configurations to consider:
1. An automatic handshake mode, e.g., V.32 bis auto [PRS HM ; 2], V.32 auto [PRS HM ; 4],
V.22 bis only [PRS HM ; 6], takes precedence over the PRS DR selection, and the modem tries
for the highest VF speed common to the two commands.
2. For 1200 bps V.22 operation, select PRS HM ; 7. PRS HM ; 6 is an auto mode, so setting the
DTE to 1200 bps (PRS DR ; 3) will not force the connection to 1200 bps.
3. When the modem is optioned for an automatic handshake mode and direct V.14 asynchronous
mode (AT command \N1), it sends a connect message to the DTE at the selected PRS DR
speed. In order to pass data, the user must change the DTE's speed to match the displayed
connect speed.
4. When the modem is optioned for speed buffering (AT command \N0) or an error correcting
protocol (AT commands \N2 through \N5), the PRS DR command alone selects the DTE
speed, and the PRS HM command selects the handshake mode.
5. When the modem is optioned for a fixed handshake mode and direct mode (AT command
\N1), the PRS DR command not only selects the DTE speed, but also forces the VF speed to
match it. If the required VF speed is not available the modem drops the call. (This does not
apply to V.22 bis only, which handshakes at the highest VF speed.)
6. When using the modem in direct mode (AT command \N1), if the desired connect speed is
known, set the speed to match using the PRS DR command. Set the DTE to the same speed
and "AT" the modem so that it will know at what speed to send messages.
Note
The modem must be in the AT command set mode in order to configure the \Nn AT command.
060R122-000
Issue 15
SpectraComm Dual V.34 Modem
Installation and Operation
Commanding the Modem
5-5
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