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Discussion Starter · #1 ·

I’m trying to build a can bus scanner for the mazda6.
The OBD connector that is located under the steering wheel column has the following signals.

4 Chassis Ground
5 Signal Ground
6 Can_High
7 ISO 9141-2 K-line
14 Can_Low
16 Battery power

In know that the can protocol requires a connection to pin5, pin6 and pin 14.
Could someone please explain why is pin7 (IOSO 9141-2) available on the obd connector since it’s not part of the CAN protocol.

4,100 Posts
Ok trying to do some research here as I want to see if I can transfer my knowledge of using multiple displays for weather data systems that use RS232 to having mutiple OBD displays such as a dashhawk and a OBD computer program. So i will use this to try and gather info and see if I get anywhere.

Puting in a carputer. Will have iguidance nav and hopefully some OBD stuff eventually to if I can figure out how to make it work while still using dashhawk (slave/master).

I dont know what kind of data it is, but like with the weather system I used to work on (WSI inflight weather) it utilized RS232 data to send the weather data from the receiver to the display and I could have multiple displays of the data so long as the slowest one was the master or you just turn hardware flow control off. Assume it is the same situation, I can have the OBD cable split and the slave (say computer OBD) would not have the "flow control" wire hooked up so it would get all the data it needed and would display fine...Iduno thou as this can bus OBD2 crap is nothing I know about...will have to join another forum as I havent seen this figured out on the MP3car forum

Bus positive Line of SAE-J1850
Ford DCL(+) Argentina, Brazil (pre OBD-II) 1997-2000, Usa, Europe, etc.
Chassis ground
Signal ground
CAN high (ISO 15765-4 and SAE-J2284)
K line of ISO 9141-2 and ISO 14230-4
Bus negative Line of SAE-J1850
Ford DCL(-) Argentina, Brazil (pre OBD-II) 1997-2000, Usa, Europe, etc.
CAN low (ISO 15765-4 and SAE-J2284)
L line of ISO 9141-2 and ISO 14230-4
Battery voltage
The assignment of unspecified pins is left to the vehicle manufacturer's discretion.

Signal protocols
There are five signalling protocols currently in use with the OBD-II interface. Any given vehicle will likely only implement one of the protocols. Often it is possible to make an educated guess about the protocol in use based on which pins are present on the J1962 connector:

SAE J1850 PWM (pulse-width modulation - 41.6 kbaud, standard of the Ford Motor Company)
pin 2: Bus+
pin 10: Bus–
High voltage is +5 V
Message length is restricted to 12 bytes, including CRC
Employs a multi-master arbitration scheme called 'Carrier Sense Multiple Access with Non-Destructive Arbitration' (CSMA/NDA)

SAE J1850 VPW (variable pulse width - 10.4/41.6 kbaud, standard of General Motors)
pin 2: Bus+
Bus idles low
High voltage is +7 V
Decision point is +3.5 V
Message length is restricted to 12 bytes, including CRC
Employs CSMA/NDA

ISO 9141-2. This protocol has a data rate of 10.4 kbaud, and is similar to RS-232. ISO 9141-2 is primarily used in Chrysler, European, and Asian vehicles.
pin 7: K-line
pin 15: L-line (optional)
UART signaling (though not RS-232 voltage levels)
K-line idles high
High voltage is Vbatt
Message length is restricted to 12 bytes, including CRC

ISO 14230 KWP2000 (Keyword Protocol 2000)
pin 7: K-line
pin 15: L-line (optional)
Physical layer identical to ISO 9141-2
Data rate 1.2 to 10.4 kbaud
Message may contain up to 255 bytes in the data field

ISO 15765 CAN (250 kbit/s or 500 kbit/s). The CAN protocol is a popular standard outside of the US automotive industry and is making significant in-roads into the OBD-II market share. By 2008, all vehicles sold in the US will be required to implement CAN, thus eliminating the ambiguity of the existing five signalling protocols.
pin 6: CAN High
pin 14: CAN Low

Note that pins 4 (battery ground) and 16 (battery positive) are present in all configurations. Also, ISO 9141 and ISO 14230 use the same pinout, thus the connector shape does not distinguish between the two.
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