Product manual
XStream‐PKG‐R™RS‐232/485RFModem–ProductManualv4.2B
©2005MaxStream,Inc.Confidential&Proprietary 33
SM Command (continued)
The modem remains in Sleep Mode for a user-defined period of time ranging from 0.5 seconds to
16 seconds (SM Parameters 3 through 8). After this interval of time, the modem returns to Idle
Mode and listens for a valid data packet for 100 ms. If the modem does not detect valid data (on
any frequency), the modem returns to Sleep Mode. If valid data is detected, the modem
transitions into Receive Mode and receives incoming RF packets. The modem then returns to
Sleep Mode after a Period of inactivity that is determined by ST “Time before Sleep” Command.
The modem can also be configured to wake from cyclic sleep when SLEEP/DI3 is de-asserted
(low). To configure a modem to operate in this manner, PW (Pin Wake-up) Command must be
issued. Once DI3 is de-asserted, the modem is forced into Idle Mode and can begin transmitting
or receiving data. It remains active until no data is detected for the period of time specified by
the ST Command, at which point it resumes its low-power cyclic state.
Note: The cyclic interval time defined by SM (Sleep Mode) Command must be shorter than the interval
time defined by LH (Wake-up Initializer Timer).
For example: If SM=4 (Cyclic 1.0 second sleep), the LH Parameter should equal 0x0B (“1.1” seconds).
With these parameters set, there is no risk of the receiving modem being asleep for the duration of
wake-up initializer transmission. “Cyclic Scanning” explains in further detail the relationship between
“Cyclic Sleep” and “Wake-up Initializer Timer”
Cyclic Scanning. Each RF transmission consists of an RF Initializer and payload. The wake-up
initializer contains initialization information and all receiving modems must wake during the
wake-up initializer portion of data transmission in order to be synchronized with the transmitting
modem and receive the data.
Figure4.3. CorrectConfiguration(LH>SM)
Lengthofthewake‐upinitializerexceedsthetimeintervalofCyclicSleep.Thereceiverisguaranteedtodetect
thewake‐upinitializerandreceivetheaccompanyingpayloaddata.
Figure4.4. IncorrectConfiguration(LH<SM)
Lengthof
wake‐upinitializerisshorterthanthetimeintervalofCyclicSleep.Thisconfigurationisvulnerable
tothereceiverwakingandmissingthewake‐upinitializer(andthereforealsotheaccompanyingpayloaddata).