Thread: OBD2 Source code for opto interface

Originally Posted by jjakes24

here is a c++ function I found that is suppose to handle the init for 5 baud:

char diag_l0_initbus(void)
{

TRISC6 = 0; //Set RC6 as output
//Now we need to sent address of 0x01 at 5 baud

OBD_K_LINE = 0;

DelayMs(200);

OBD_K_LINE = 1;

DelayMs(200);

OBD_K_LINE = 0;

DelayMs(200); //A high of 1400mS
DelayMs(200);
DelayMs(200);
DelayMs(200);
DelayMs(200);
DelayMs(200);
DelayMs(200);

OBD_K_LINE = 1;

//Now config serial port
SPBRG=29; // data rate for sending/receiving @ 10400 baud
BRGH=0; // data rate for sending/receiving
SYNC=0; // asynchronous
SPEN=1; // enable serial port pins
CREN=1; // enable reception
SREN=0; // no effect
TXIE=0; // disable tx interrupts
RCIE=0; // disable rx interrupts
TX9=0; // 8-bit transmission
RX9=0; // 8-bit reception
TXEN=1; // enable the transmitter

}

from http://www.skpang.co.uk/ecu_reader.htm

You know that's for a PIC Microcontroller right?

Originally Posted by Maddog_rvo

Yup, but its good for looking how to initialize connection to the ECU

But pretty much all that code is to set up the PIC's UART, not the ECU.

The reason that most readers are slow, is there's a 20ms delay between queries. That's part of the specs I believe. If you could cut that down, then they would update faster. Wether this would cause problems on your vehicle, who knows.

Do you know what interface your car is using? Is it ISO 9141? That's K-Line.

Your best bet is to look at what docs are available for your specific interface.

Originally Posted by Maddog_rvo

Its iso 9141 indeed, i think with the current code the init succeeds, but i now get a framing error as soon as data is received, which crashes my app. Does anyone know what kind of error this is and how to solve it?

Probably a timing error. There are certain timings that need to be adhered to ,etc. If you don't know learn what needs to be done, it's probably going to be extremely difficult to probe around until you happen to make something work.

If you don't want to try and read up on the interface, take a look at freediag and see if you can grok enough of it to get something working.