User’s Guide | Advanced Features |
Assign a Channel
The command +WPCHAN can be used to force the modem to lock on a particular channel, typically for diagnostic purposes. When set to a specific channel, it overrides the setting of Side Preference but does not override the settings in the SPNI list (both discussed below).
If you assign a channel and it is acquired, the modem will use that channel for registration attempts. If registration fails on the assigned channel NO automatic attempts are made to locate another channel. This is highly discouraged. Locking to a specific channel deviates from the CDPD specification.
Changing the channel assignment while the modem is registered will not change the registration status. The modem may lose connectivity if the new channel does not present sufficient signal or fails to meet other requirements such as SPNI matching.
If the cellular carrier forces CDPD channel hopping (part of the CDPD specification) the modem will follow the hops regardless of the user assigned channel.
To assign a channel for use by the modem issue the AT command +WPCHAN=n where n is the channel number to assign. The modem will go to that channel. Subsequent use of +WPRSSI will report the strength of signal and if the channel has been acquired.
Auto-locate a Channel
This is the default setting of the modem.
To have the modem locate a channel, issue the AT command +WPCHAN=0. The modem will then scan for a channel when requested to register (or
7.2.1.2.Side Preference
The modem scans for channels based on a side preference set in register +WS174. The settings are as follows:
1 – A side preferred,
2 – B side preferred,
3 – A side only,
4 – B side only.
NOTE
The channel side preference is stored in a register not associated with a particular entry in the NEI table. The preference will be used for all NEI registrations.
The service provider will have advised you of the channel side they use. Settings of 1 or 2 are encouraged over settings of 3 or 4 if the modem is to be mobile. For “preferred” settings, the modem will first scan for channels on the side specified, but if a suitable channel is not found, the other side channels will also be scanned. Note that the modem may stay on the alternate side as long as usable CDPD channels are found there; it does not periodically check for usable channels on the preferred side.
7.2.1.3.SPNI Matching
Once a suitable channel is found, the modem can optionally verify which carrier is providing service on that channel.
If you want to restrict the modem to only using channels belonging to a
2110212 Rev 1.0 | Page 55 |
