User's Guide

User’s Guide CDPD Operation
2110059 Rev 1.0 Proprietary and Confidential Page 37
5.5. Sleep Mode
CDPD provides a facility to allow modems to go to “sleep” when they do not have active
communications. This allows the modems to shut down hardware to reduce power consumption.
When the modem is waiting for data from either the host or network end, it does not need to keep
all hardware systems running. The CDPD network sends a periodic message to registered IP
addresses to advise if there is pending traffic on the network for them. The modem can be
programmed to shut down the receiver (go to sleep) between these messages, and wake up at the
defined intervals to check if the network has traffic. If there is no pending traffic, then the receiver
can go back to sleep until the next scheduled notification message.
The SB300 Series modems can use this feature and have added an additional feature called “logic
sleep” to further reduce power consumption.
5.5.1. CDPD Sleep
This is what is meant by the general term “sleep” mode. It is controlled by setting register
+WS175 (CDPD Sleep Idle Time).
Setting the register to 0 (zero) will disable sleep mode. The modem will keep the receiver active
for immediate handling of any incoming traffic from the network.
Sleep is enabled by setting the register to the time in seconds, from 10 to 3600 (1 hour), during
which the modem must have no traffic. Provided there is no traffic to or from the network during
that interval, the modem will begin using CDPD sleep.
Once sleep mode is engaged, the modem logic will turn off the radio receiver. It will turn on the
receiver at the intervals prescribed to check for traffic. If there is traffic, the modem will then deal
with it.
The disadvantage to sleep mode is that traffic from the network will have to wait up to a
maximum of one minute for the next notification cycle before the modem can receive it. This can
slow down response in some time critical applications.
While sleeping, the modem logic is ready to receive data from the host at any time. The modem
will immediately wake up for host generated traffic.
5.5.2. Logic Sleep
In addition to switching off the radio for CDPD sleep, the modem can be placed in a logic sleep
mode. This further reduces the power consumption of the modem. Logic sleep will not engage
unless CDPD sleep is already engaged.
Logic sleep will automatically engage (if it is enabled) when the modem is inactive. This can
engage after executing an AT command and before the next command is issued. The modem can
also go into logic sleep while in auto-answer mode. The modem will wake-up periodically as part
of the CDPD sleep operation to check the network for messages. Incoming data amounts to a
RING when auto-answer is enabled, so the modem will be awake to receive messages.
This feature is controlled with register S31 (Logic Sleep). Setting the register to 0 (zero) will
disable logic sleep. Setting it to 1 will enable normal logic sleep. In this condition the modem
will reduce power until the host sends a command or CDPD sleep operation requires activity. It
will wake as soon as a character arrives from the host, or automatically as needed to make periodic
network checks for traffic.
Setting the Logic Sleep register to 2 will enable deep-sleep. This will cause the modem to shut
down even more hardware, conserving even more power. The disadvantage to this is that the
modem will lose the first incoming character from the host (DTE). In fact, the modem will take
80 milliseconds, from the start of the first incoming character, to wake up. The host must be