Old tests and informations about serial communication are to be found here:


Go over this checklist, and document your measurements.

-> thanks, I answered all the Q. I hope you can help me to deduce something from all these values ;-)

-> It works great, I get my signal back when loopbacked (small wire on the end of my serial cable, it also means that my cable is ok)

-> Computer configuration, com port number are ok


-> I tried this without results. I placed a jumper on Pin1 Pin2 from Socket SV2, powered on, waited 10 secs, removed jumper, placed serial cable and tried to communicate usinf bray terminal and 19200,8,n,1 and 9600

-> serial communication doesn't work


-> Ok I measured voltage between SV2 pins and GND:

ECU SV2 pin#DSUB pin#DSUB functionVoltage between GND and SV2 pin
This is a little bit too high, if I refer to GenBoard/BuildProcedures/SerialPort

-> the same, with a wire pulling down SV2 pin# to GDN:

ECU SV2 pin#DSUB pin#DSUB functionVoltage between GND and SV2 pin

-> wire pulling up to +4,99V (uC power)

ECU SV2 pin#DSUB pin#DSUB functionVoltage between GND and SV2 pin

I also tried different things on the uC:

  • you can also measure the max232 pins, you should find +8V on one pin and -8V on another
pin number#12345678910111213141516
voltage between GND and pin#+4,92V0V-8,55V0V+4,92+3,8V+3,81V+4,92V+6,8V+8,89V+2,3V+4,42V-4,51V-8,57V-8,57V0V
Here is a picture to explain my pin numbers:


  • measure DC voltage on the xtal pins (should be near 2.5V)
-> I measured voltage between the 2 Xtal pins and I have 0V with power connected. I'm surprised of this result. A friend of mine had taken the board to try to help and had told me that Xtal was OK. This is where i measured:


If all else fails, you can try if you can get ISP communications to the processor as on GenBoard/Firmware/Upload. The ISP is a simple, short 5pin "stk200" cable connected to parallelport (DSUB25). avrdude is the most frequently used application (uisp is another option). The ISP should work if the microcontroller gets supply and not blown. in avrdude -c stk200 -p m128 -t try some commands like (just examples by memory, see avrdude manual and try to capture in file)

The bootloader communications also requires the xtal, the max232 (and it's connections) and the fuses inside the avr, and bootloader flash-area (0x1f800 .. 0x1fff0) inside the AVR (which is unlikely to damage: possible eg. by replacing the processor with a new one ;-)

-> I had already built the cable, using the information found on MembersPage/MattiasSandgren/NickesBMW/AvrBootCode.

So here is the cable schematics:

AVR pin commandISP header #Parallel port pinNotes
AVR /RESET57Yellow
AVR SCK (clock input)38Black
AVR PDI (RXD) (instruction in)49Red
AVR PDO (TXD) (data out)110Orange
Signal Ground618Brown

I also checked that each pin of JP_ISPI is connected to the matching pin on the uC. and drew this schematic:


So it doesn't work.