ScanTool STN11xx - Manual (Page 4)

STN11xx PowerSave
randomly toggle the UART communication lines and
can unintentionally wake up the device as they are
shutting down or entering the standby mode.
1.2.2 UART Inactivity
The STN11xx can be configured to go to sleep
automatically after a period of UART inactivity.
UART inactivity sleep trigger is turned on/off
using the STSLU command (it is off by default). Use
the STSLUIT command to set the UART inactivity
sleep timeout.
Warning: STN11xx UART inactivity sleep trigger is
disabled while any command is executing. In other
words, STN11xx must print the command prompt
before it will act on a sleep trigger. Therefore,
commands which require UART activity to terminate
their execution (e.g., ATMA, STMT, etc) will keep the
device awake indefinitely. A continuous stream of
incoming messages may also prevent the device from
going to sleep. This may occur, for example, if
message filters are set up to accept bus traffic
intended for other nodes.
1.2.3 External SLEEP Input
Another automatic sleep trigger is the external
SLEEP input. This trigger is off by default. When
enabled (using the STSLX command), it allows the
external circuitry to control the sleep state.
When STN11xx senses a logic low on the SLEEP
pin, it immediately aborts any OBD reception in
progress, or monitoring command that is active at the
time, and prints the command prompt. It then monitors
the SLEEP input and enters the PowerSave mode if
the minimum low time (specified by the STSLXST
command) is satisfied.
Note: STN1110 and microOBD 200 (STN1120)
allow the polarity of the external SLEEP input to be
inverted, via the STSLXP command.
The following are some of the possible uses of this
trigger:
• “Host present” detect – sleep/wakeup
when the host disconnects/connects or
starts up/shuts down (goes into standby)
• Ignition key detect – sleep/wakeup
depending on the ignition key position
• Direct sleep control via host
microcontroller
The logic state of the SLEEP input state can be
polled using the STSLXS and ATIGN commands.
See section 1.6 for device-specific implementation
details.
1.2.4 Voltage Level Sleep
The STN11xx can also enter sleep mode based on
the voltage on the ANALOG_IN input. This trigger can
be configured in the variety of ways. The settings
specify voltage threshold, whether the trigger is active
above or below the threshold setting, and the amount
of time the voltage must stay below or above the
threshold for the device to enter sleep mode.
The voltage level sleep trigger can be used to put
the device into the low power mode when the engine
shuts down and the alternator stops generating power.
The delay is designed to prevent the device from
entering sleep when the system voltage dips below the
specified threshold due to momentary load changes.
The default settings should work for most vehicles with
12 volt lead-acid batteries.
Use the STSLCS command to verify that the trigger
was properly configured. An exclamation point (‘!’) in
front of the voltage setting means that the trigger
setting is invalid, and the trigger will never activate.
Refer to section 1.4 “Voltage Trigger Considerations”
for more information.
Note: In order for the voltage level sleep trigger to
operate properly on STN1110 IC or the microOBD 200
module (STN1120), the voltage measurement must be
calibrated using the ATCV or STVCAL commands. The
calibration is not necessary for the OBDLink scan
tools, since it is done at the factory.
1.3 Wakeup Triggers
There are four wakeup triggers:
• UART Rx pulse (SLU)
• External SLEEP input (SLX)
• Voltage level (SLVL)
• Voltage change (SLVG)
After any wakeup trigger timing requirements are
satisfied, the STN11xx will wake up and perform an
ATWS reset. The wakeup takes several milliseconds,
therefore the host must wait for the command prompt
before issuing any commands.
The STSLLT command can be used to determine
which trigger caused the device to wake up.
By default, UART Rx pulse and external SLEEP
input wakeup triggers are on, and voltage triggers are
off.
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