ELM329
Pin Descriptions (continued)
be the most positive point in the circuit. Internal
circuitry connected to this pin is used to provide
power on reset of the microprocessor, so an external
reset signal is not required. Refer to the Electrical
Characteristics section for further information.
M1
(pin 21) and
M0
(pin 22)
These two output pins are provided for use with CAN
transceiver ICs, as are typically used for Single Wire
CAN applications. The ELM329 will set both outputs
to a high level (‘Normal’) after startup, but the level at
these pins may be changed at any time with the
AT TM commands, and the level after powerup may
be set with PP20.
CAN Tx
(pin 23) and
CAN Rx
(pin 24)
These are the two CAN interface signals that must
be connected to a CAN transceiver IC (see the
Example Applications section for more information).
If unused, pin 24 must be connected to a logic high
(V
DD
) level.
RS232 Rx LED
(pin 25),
RS232 Tx LED
(pin 26),
OBD Rx LED
(pin 27) and
OBD Tx LED
(pin 28)
These four output pins are normally high, and are
driven to low levels when the ELM329 is transmitting
or receiving data. These outputs are suitable for
directly driving most LEDs through current limiting
resistors, or interfacing to other logic circuits. If
unused, these pins may be left open-circuited.
Note that pin 28 can also be used to turn off all of the
Programmable Parameters, if you can not do so by
using the normal interface - see page 61 for more
details.
Unused Pins
When people only want to implement a portion of what the ELM329 is capable of, they often ask what to do with the
unused pins. The rule is that unused outputs may be left open-circuited with nothing connected to them, but unused
inputs must be terminated. The ELM329 is a CMOS integrated circuit that can not have any inputs left floating (or
you might damage the IC). Connect unused inputs as follows:
Pin
Level
1
H
2
*
5
*
6
*
7
*
11
*
12
*
13
*
15
H
18
H
24
H
The inputs that are shown with an asterisk (*) may be connected to either a High (V
DD
) or a Low (V
SS
) level.
Absolute Maximum Ratings
Storage Temperature....................... -65°C to +150°C
Ambient Temperature with
Power Applied....................................-40°C to +85°C
Voltage on V
DD
with respect to V
SS
..... -0.3V to +7.5V
Voltage on any other pin with
respect to V
SS
........................... -0.3V to (V
DD
+ 0.3V)
Note:
These values are given as a design guideline only.
The ability to operate to these levels is neither
inferred nor recommended, and stresses beyond
those listed here will likely damage the device.
ELM329DSB
Elm Electronics – Circuits for the Hobbyist
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