ScanTool STN1100 FRPM - Manual (Page 19)

Family Reference and Programming Manual
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10.2.3 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 ATIGN and STSLXS commands.
See section 10.5 for device-specific implementation
details.
10.3 Wakeup Triggers
There are two wakeup triggers that are available:
UART Rx pulse and external SLEEP input.
After any wakeup trigger timing requirements are
satisfied, the STN11xx will wake up and perform an
ATWS reset. The wakeup takes several milliseconds,
so 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.
Both wakeup triggers are on by default.
10.3.1 UART Rx Pulse Wakeup
STN11xx can be configured to wake up on an
active pulse detected on the UART Rx input. The host
can generate the pulse by holding the Rx line in a logic
low state, transmitting an RS232 “break” signal, or
sending a character on UART whose bit pattern
produces a pulse of the required duration.
The wakeup pulse has minimum and maximum
timing requirements, which are set using the
STSLUWP command, and are accurate to within
approximately 5 μs. By default, the minimum wakeup
pulse width is set to 0, which translates to an absolute
minimum pulse width requirement of 20 ns. It can be
increased to improve noise rejection; however,
increasing the minimum pulse width will limit the
maximum baud rate that the host must use to transmit
the wake-up character. Due to the implementation
limitations, setting the minimum wakeup pulse width to
any value below 15 μs will cause it to be rounded down
to 0.
The purpose of the maximum wakeup pulse
width requirement is to avoid unintentional wakeups.
Some PC hosts (especially ones using the RS232
connection) cause the UART Rx line to go low or
generate a slow (200 ms or longer) pulse as the host is
shutting down or entering standby. The default setting
is 30 ms, which allows the device to wake up on a
character transmitted over UART at baud rates as low
as 300 baud. To disable the maximum pulse
requirement and have ST11XX wake up on the high to
low UART Rx transition (instead of a pulse), set the
maximum pulse timing setting to 0.
10.3.2 External SLEEP Input Wakeup
STN11xx can be configured to wake up when it
senses a logic high on the external SLEEP control
input.
The STXWT commands sets the minimum time the
SLEEP input must remain high in order to bring the
device out of the sleep state. The setting of 0 will result
in a minimum time requirement of 15 μs.
Note: STN1110 and microOBD 200 (STN1120)
allow the polarity of the external SLEEP input to be
inverted, via the STSLXP command.
Section 10.2.3 lists some useful applications for the
external SLEEP input.
10.4 External Power Control Output
The PWR_CTRL output can be used to put
external circuitry into a low power mode. This pin
outputs a logic “high” while the device is awake, and a
“low” when STN11xx enters sleep mode.
Note: STN1110 stand-alone IC allows the polarity
of the PWR_CTRL to be changed via the STSLPCP
command or bit 6 of the 0E programmable parameter
(ELM327 LP mode only). The polarity is fixed for all
other STN11xx ICs.
10.5 Device Specific Details
This section describes device-specific PowerSave
implementation details for the different STN11xx-based
devices.
10.5.1 OBDLink Rev 1.x
OBDLink devices with hardware revision 1.x have
the following limitations: