DCD/DTR/DSR signals, loopback test, connector layout, component choice

Hi,

I got the adapter running with
VAG-COM 0.50a (free beta from www.ross-tech.com/vag-com)
notebook Toshiba Tecra 8000
old style 2x2 interface with K and L line
VW T4 1992 AAF engine
ECU Digifant 1.2.

At first VAG-COM replied with 'Adapter not ready' both under
options/test and select/engine.

Solution:
Connect DCD, DTR and DSR (Pins 1, 4, 6) of the RS-232
interface. [If these signals are not used in a fully wired
DTE-DTE connection, they must be connected together].

Jeff described a way to test the adapter with a terminal program
(loopback over the K-section, it does not test the L-section). I had
no success with this method (I tried three different notebooks). RTS
was always high and therefore reception disabled regardless of the
flow control used. Perhaps there are serial interface chips or drivers
where RTS defaults to low, when the flow control is disabled and it
works. In general it does not. Nevertheless it's a good way to test
the adapter.

Solution:
If RTS is always high with your notebook just disconnect it
from the RS-232 connector and tie it to ground during the
test.

By the way, in my car it was like this:

|-\ /-\
|+| grey/white, K |+| red, 12V
|+| yellow, L |+| brown, ground
|-/ ---

It's a good idea to place a Diode in the +12V feed of the adapter.
This prevents potential damage if the power supply is not connected
correctly.

Optoisolators and transistors are not critical. Any small signal
stuff will do it. I use Sharp PC847 and BC237. The notebook has to
drive sufficent current into the diodes of the optoisolator. If the
notebook has output voltages significently lower than +-5V try to
lower the 1K-resistances in series with the diodes.

Thanks a lot to Jeff Noxon for his effort, his web page and support.

Have fun!
Arnold

--------------------------------------------------------------------
Jeffs loopback test:
Connect the adapter to your laptop. Connect a 12V battery (not your
car) to the power/ground pins of the OBD-II side of the adapter.
Run a program like Hyperterminal, with flow control disabled, full
duplex, direct connect to com1, 19200 bps. Anything and everything
you type should echo back to the screen. If not, something is wrong.
Check 38400 bps also. If it misses or changes characters, your laptop
may have insufficent voltage (check the +/- ranges with a volt/ohm
meter), or your optoisolators may not have sufficent bandwidth.

 
Received on Wed Aug 30 00:38:05 2000