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CAN (Single Wire) Transceiver Modes
The ELM329 was designed with two wire CAN
(OBDII) applications in mind, but there is no reason
that it can not be used for single wire CAN applications
(SAE J2411, etc.), as well. The data format remains
much the same on the CAN networks - it is really the
physical interface that differs.
Single wire CAN transceiver chips are available
and should be used when connecting the ELM329 to
single wire CAN networks. These ICs usually provide
mode inputs which are used to change the state of the
device - to put it into low power sleep mode, set the
output to high voltage (12V) mode, etc. The table
below shows the four modes typically supported by
single wire CAN transceiver ICs, and the mode inputs
most often used for each.
TM
#
M1
(pin 21)
M0
(pin 22)
Mode
0
1
2
3
Sleep
High Speed
High Voltage Wakeup
Normal
0 0
1
1
1 1
0
0
The ELM329 provides two output pins (M0 and
M1) that may be used to set the modes for a single
wire CAN transceiver. After every reset or AT D
command, the level at pins 21 and 22 will be set
according to PP 20. Note that firmware v1.0 set these
pins to a low level (mode = sleep) when the IC went to
low power mode, but the ELM329 no longer changes
the setting while in low power mode.
The M0 and M1 pin levels are controlled with the
Transceiver Mode commands. For example, if you
wish to put the transceiver into the high voltage
wakeup mode, simply send;
>AT TM 2
OK
and to restore the mode to normal, send:
>AT TM 3
OK
If you do not require these pins for a single wire
CAN application, they may be used as general
purpose outputs., much like the Control output.
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