INFO.self-diagnos OBD.II

[BERNT FRISK]

--HELLO!

I hope that this could be of interest for DIY_EFI list readers.


The increasing number of electronic controllers in motor
vehicles have made self-diagnosis a necessity. In order to 
make diagnosis work easier for the mechanic.

Bosch has decided on the procedure described in the following.

A unidirectional line (L line) is used for addressing, the line
for data interchange (K line) is bidirectional, so that only
one diagnosis connecter need to be fitted per vehicle,botk the
K and L lines had to be connectable to all controllers (bus).

The electrical specifications are as follows.

                    L line spec.

The terminal leads to an input circuit for switching signals
A network of 10 controllers forms the basis for the specification.
Vb = supply voltage at controller

Parameter              conditions   Rem   Min     Max     unit

input V. high                        1    0.8Vb   Vb+1     Volts
input V. low                               -1     0.2Vb    volts

input resistance                     2     50              K.ohms
input capacitance        C1                       500      Pf

Remarks:
1) for short periods max 40 Volts
2) leads to a countervoltage of min 0.8 Vb
C) C1 = interference immunity

                    K line spec.

An input and output circuit are connected to this terminal at
the same time.
Output : "open collector" with pull-up resistor as per Vb
Input  :  flip-flop with threshold detector behavior

A network of 10 controllers forms the basis for the specification.

Vb = supply voltage at the controller input/output short-circuit-
proof to Vb and ground.


Parameter              conditions       rem   min   max   unit

output volt low        Io= 10mA                     1.1   volts
                       Io= 13mA                     1.4   volts
                       Io= 25mA                     2.7   volts

Fall time              Vo= 0.8Vb..0.2Vb  1          0.1/BR  S
pull-up resistor                         2    95          K-ohms
leakage resistor       output stag high- 4    50          K-ohms
                       impedance

input volt. high                         3    0.8Vb Vb+1  volts
input volt. low                               -1    0.2Vb volts
input capacitance      C1                5          500    Pf

Remarks:

1) external load capacitance :10 nf max.
   BR = baud rate of transmission
2) to Vb
3) for short periods max. 40 volts
4) to ground
5) other values are only allowable if a written customer request
has been submitted.

Best regards:
 Bernt