User's Manual

MaxStream, Inc. 24XStream Wireless Module Manual v2.8
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period can be set by adjusting the ST parameter (see the ‘ST’ command in “24XStream
Command Table”). The module remains in Sleep Mode for a user-defined period of time ranging
from 0.5 seconds to 8 seconds (adjustable using ‘SM’ command as described in “24XStream
Command Table” section). After this period of time, the module returns to Idle Mode and listens
for a valid data packet. If no valid data packet is found on any channel, the module returns to
Sleep Mode. If a data packet is found, the module transitions into Receive Mode and receives the
incoming packets until another ST inactivity time out. When the module is awake, it requires 100
milliseconds to search for a valid data packet.
While the module is in its low-power state, the *CTS pin (Pin 1) is driven high (de-asserted) to
indicate that data should not be sent to the module during this time. When the module awakens to
listen for data, the *CTS pin is asserted, and any data received on the DI pin will be transmitted.
The TX/PWR pin (Pin 8) is driven low (de-asserted) when the module is in Cyclic Sleep Mode.
It is asserted each time the module cycles into Idle Mode to listen for valid data packets, and then
de-asserts if the module returns to Sleep Mode.
A Note About Cyclic Scanning
Each RF packet consists of a header and data as shown previously in Figure 5b. Since the header
contains the channel synchronization information, the module must wake up during the header
portion of a packet in order to synchronize with the transmitter and receive the data. To ensure
that the 24XStream module can detect the header, a long header can be sent periodically during a
transmission. This long header repeats the synchronization information for a period of time
defined by the ‘LH’ command.
By default the long header is turned off, and must be enabled in order to communicate with a
module operating in Cyclic Sleep Mode. To enable the long header, the LH parameter must be
set to a value greater than the time of cyclic sleep to ensure accurate detection by the receiver(s).
For example, if the 24XStream is set to wake up from Sleep Mode every four seconds and check
for a packet, a transmitter would need to send a long header that is just over four seconds in
length to guarantee that the receiving module will detect the packet. (The exact timing
requirements can be found in the Timing Diagrams section.) This concept of long header length
versus Sleep Mode timing is displayed in Figure 7 below.
Figure 7a – The length of the long header is
not as long as the period of Cyclic Sleep. It is
possible for the receiver to wake and miss the
header (and the data packet) in this scenario.
Figure 7b – The length of the long header
exceeds the period of Cyclic Sleep. The
receiver is guaranteed to detect and receive the
data packet.
The long header is only sent with the initial transmitted packet after a user-defined period of
inactivity (no serial data received and no over-the-air transmitting or receiving). This period of
inactivity must be adjusted using the ‘HT’ command as described in the “24XStream Command
Table”. Sending the long header assures that the receiver will detect the new transmission and
will be able to receive the data as long as the header length slightly exceeds the cyclic sleep time.