WCM802/900
20
JUN
2005
PAGE
25
HT (Time before Wake-up Initializer) Command
<Sleep (Low Power)> If any modules within
range are running in a “Cyclic Sleep” setting, a
wake-up initializer must be used by the
transmitting module for sleeping modules to
remain awake [refer to the LH (“Wake-up
Initializer Timer”) Command]. When a receiving
module in Cyclic Sleep wakes, it must detect the
wake-up initializer in order to remain awake and
receive data. The value of HT Parameter tells the
transmitter, “After a period of inactivity (no
transmitting or receiving) lasting HT amount of
time, send a long wake-up initializer”. HT
Parameter should be set to match the inactivity timeout [specified by ST (Time before Sleep)
Command] used by the receiver(s).
From the receiving module perspective, after HT time elapses and the inactivity timeout [ST
Command] is met, the receiver goes into cyclic sleep. In cyclic sleep, the receiver wakes once per
sleep interval to check for a wake-up initializer. When a wake-up initializer is detected, the
module will stay awake to receive data. The wake-up initializer must be longer than the cyclic
sleep interval to ensure that sleeping modules detect incoming data. When HT time elapses, the
transmitter then knows that it needs to send a long Wake-up Initializer for all receivers to be able
to remain awake and receive the next transmission. Matching HT to the time specified by ST on
the receiving module guarantees that all receivers will detect the next transmission.
ID (Module VID) Command
<Networking> Read the module’s VID. VID is a
Horner-specific acronym that stands for “Vendor
Identification Number”. This number is factory-
set and allows modules with matching VIDs to
communicate. Modules with non-matching VIDs
will not receive unintended data transmission.
LH (Wake-up Initializer Timer) Command
<Sleep (Low Power)> LH Command adjusts the
duration of time for which the RF initializer is
sent. When receiving modules are put into Cyclic
Sleep Mode, they power-down after a period of
inactivity [specified by ST (Time before Sleep)
Command] and will periodically awaken and listen
for transmitted data. In order for the receiving
modules to remain awake, they must detect
~35ms of the wake-up initializer.
LH Command must be used whenever a receiver
is operating in Cyclic Sleep Mode. This lengthens
the Wake-up Initializer to a specific amount of time (in tenths of a second). The Wake-up
Initializer Time must be longer than the cyclic sleep time that is determined by SM (Sleep Mode)
Command. If the wake-up initializer time were less than the Cyclic Sleep interval, the connection
would be at risk of missing the wake-up initializer transmission.
Refer to Figures 4.3 & 4.4 of the SM Command description to view diagrams of correct and
incorrect configurations. The images help visualize the importance that the value of LH be greater
than the value of SM.
AT Command: ATHT
Binary Command: 0x03 (3 decimal)
Parameter Range: 0 – 0xFFFF
[x
100
milliseconds]
Default Parameter Value: 0xFFFF (means that
long wake-up initializer will not be sent)
Number of bytes returned: 2
Related Commands: LH (Wake-up Initializer
Timer), SM (Sleep Mode), ST (Time before
Sleep)
AT Command: ATID
Binary Command: 0x27 (39 decimal)
Parameter Range (user-settable):
0x10 - 0x7FFFF
(Factory-set and read-only) : 0x8000 – 0xFFFF
Number of bytes returned: 2
Minimum Firmware Version Required: 4.2B
(Previous versions did not support user-
settable VIDs)
AT Command: ATLH
Binary Command: 0x0C (12 decimal)
Parameter Range: 0 – 0xFF
[x
100
milliseconds]
Default Parameter Value: 1
Number of bytes returned: 1
Related Commands: HT (Time before Wake-up
Initializer), SM (Sleep Mode), ST (Time before
Sleep)