ELM329
Low Power Mode (continued)
The final method to wake the ELM329 is with a
low to high signal level transition at the IgnMon input. If
this is wired (through resistors) to a 12V signal that is
controlled by the ignition switch, then turning on the
ignition will also turn on the ELM329 circuit.
No matter how the ELM329 is brought back to full
power operation, it will always restore pin 14 first,
followed 50 msec later by pin 16, and then it will wait 1
second before proceeding with the startup. This 1 sec
period gives your external circuitry a little time to start
up before being expected to be fully functional. After
the 1 second period, the ELM329 will perform a partial
warm start (AT WS) and be ready for operation. We
say partial because several settings are not altered by
the wakeup (they were with v1.0). The settings that
remain unchanged are:
AT0, AT1, AT2 CAF0, CAF1
CEA
CFC0, CFC1
E0, E1
CSM0, CSM1 D0, D1
JTM1, JTM5
M0, M1
H0, H1
R0, R1
L0, L1
S0, S1
In addition, the protocol number is not reset (but
the protocol is closed).
This has discussed some of the aspects of using
the Power Control feature, from a logical perspective.
Also refer to the ‘Modifications for Low Power Standby
Operation’ section (page 66) for some of the electrical
design considerations.
CAN was active
before low power
b3*
CAN Monitor
(pin 11)
activity
monitor
rising edge
) detector
(
low level
at input
RS232 Rx
(pin 18)
1 sec
delay
(partial)
warm start
128 µsec min
pulse width
Go to
Full Power
b1
IgnMon
(pin 15)
1 or 5 sec
delay
rising edge
) detector
(
Figure 7. Returning to Normal Operation
ELM329DSB
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