ELM329L
Pin Descriptions (continued)
wish it to monitor that signal, and possibly control the
low power operation based on it.
will always restore normal operation, regardless of
the setting of PP 0E bit 2, or whether pin 15 was the
initial cause for the low power mode. This feature
allows a system to control how and when it switches
to low power standby operation, but still have
automatic wakeup by the ignition voltage, or by a
pushbutton.
If no CAN signal is detected, the ELM329 assumes
that you are using this pin to control the behaviour of
the Active LED output when the IC is in the low
power mode (as it did for v1.0 ICs). In this mode, if
pin 11 is at a high level when low power operation
begins, the Active LED output will flash for about
16 msec every 4 seconds. If the input is at a low
level when low power operation begins, the
Active LED output will be off (high) when in low
power mode. If a CAN signal was detected on pin
11, the operation of the Active LED during low power
is determined by PP 0F, bit 4.
If either bit 7 or bit 2 of PP 0E are ‘0’, this pin will
function as an active low ‘Request To Send’ input.
This can be used to interrupt the OBD processing in
order to send a new command, or if connected to
ignition positive, to highlight the fact that the ignition
has been turned off. Normally kept at a high level,
this input is brought low for attention, and should
remain so until the Busy line (pin 16) indicates that
the ELM329 is no longer busy, or until a prompt
character is received (if pin 16 is being used for
power control).
Monitoring for a CAN signal (ie. transitions at this
input pin) is a continuous background process that
can not be disabled.
In1 and In2 (pins 12 and 13)
This input has Schmitt trigger wave shaping. By
default, pin 15 acts as the RTS interrupt input.
These two inputs may be used for the monitoring of
logic level signals. Simple AT commands may be
used to read the level at either pin. No special
amplification is required, as the inputs have Schmitt
trigger wave shaping.
PwrCtrl / Busy (pin 16)
This output pin can serve one of two functions,
depending on how the Power Control options
(PP 0E) are set.
PwrCtrl (pin 14)
If bit 7 of PP 0E is a ‘1’ (the default), this pin will
function as a Power Control output. The normal state
of the pin will be as set by PP 0E bit 6, and the pin
will remain in that state until the ELM329 switches to
the low power mode of operation. This output is
typically used to control enable inputs, but may also
be used for relay circuits, etc. with suitable buffering.
The discussion on page 80 (‘Modifications for Low
Power Standby Operation’) provides more detail on
how to use this output.
This output provides a level that is the inverse of that
of the PwrCtrl output (pin 16). If the low power mode
is disabled (ie if bit 7 of PP 0E is set to ‘0’), this
output still provides the inverse of the level set by
PP 0E b6. To provide a ‘soft start’ feature, pin 14 will
always change state 50 msec before pin 16.
IgnMon / RTS (pin 15)
This input pin can serve one of two functions,
depending on how the Power Control options
(PP 0E) are set.
If bit 7 of PP 0E is a ‘0’, pin 16 will function as a
‘Busy’ output, showing when the ELM329 is actively
processing a command (the output will be at a high
level), or when it is idle, ready to receive commands
(the output will be low).
If both bit 7 and bit 2 of PP 0E are set to ‘1’, this pin
will act as an Ignition Monitor. This will result in a
switch to the low power mode of operation, if the
input goes to a low level, as would happen if the
vehicle’s ignition were turned off. An internal
‘debounce’ timer is used to ensure that the ELM329
does not shut down for noise at the input.
By default, pin 16 provides the PwrCtrl function.
RS232Tx (pin 17)
This is the RS232 data transmit output. The signal
level is compatible with most interface ICs (the
output is high when idle), and there is sufficient
current drive to allow interfacing using only a PNP
transistor, if desired.
When the voltage at pin 15 is again restored to a
high level, and a time of 1 or 5 seconds (as set by
PP 0E bit 1) passes, the ELM329 will return to
normal operation. A low to high transition at pin 15
5 of 87
ELM329L DSA
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