Connection interface of an information receiving part of a station in a differential information transmission system through two transmission lines, in particular in an automobile vehicle

This interface includes three comparators, the inputs of the first comparator being connected to the two transmission lines, one of the inputs of the second comparator being connected to one of the transmission lines and the other input of this comparator being connected to a bias voltage generator, one of the inputs of the third comparator being connected to the other transmission line and the other input of this comparator being connected to the bias voltage generator. The outputs of the comparators are connected to inputs of a multiplexer whose output is connected to the remainder of the circuits of the station, and the control inputs of the multiplexer are connected to the output of defect detecting means for detecting defects of one of the transmission lines so that the transmission lines control the multiplexer in such manner that the multiplexer selects the output of one of the comparators as a function of the state of the transmission lines.

The present invention relates to information transmitting devices in 
particular in automobile vehicles, and it more particularly concerns a 
connection interface of an information receiving part of a station in a 
differential information transmitting system through two transmission 
lines. 
A certain number of multiplexing systems are known in the art which permit 
connecting functions termed "body elements" to a central unit of the 
automobile vehicle which controls the operation. 
These elements are interconnected through two information transmitting 
lines which thus constitute a connection bus. 
For safety reasons, it is arranged that the present systems be capable of 
operating in a deteriorated mode, i.e. that the systems be capable of 
operating even if one of the two information transmitting lines is 
connected to the ground, to the potential of the battery or simply cut. 
However, this type of devices has a number of drawbacks in that, when they 
operate, it is impossible to know whether they operate normally or in a 
deteriorated mode. 
Furthermore, certain devices are also equipped with capacitive connections 
which do not permit, or permit with difficulty, utilizing collision 
dialogue systems which are still termed bus collision systems. 
An object of the invention is therefore to solve these problems by 
proposing a connection interface which permits detecting whether one of 
the two transmission lines is out of order and which also permits 
eliminating the capacitive connection of some of the transmission devices 
known at the present time and therefore rendering their operation with 
collision buses possible. 
The invention therefore provides a connection interface of an information 
receiving part of a station in a differential information transmitting 
system through two transmission lines, in particular of an automobile 
vehicle, said interface comprising three comparators, the inputs of the 
first comparator being connected to the two information transmission 
lines, one of the inputs of the second comparator being connected to one 
of the transmission lines, and the other input of this comparator to a 
bias voltage generator, one of the inputs of the third comparator being 
connected to the other transmission line and the other input of this 
comparator being connected to the bias voltage generator, the outputs of 
the comparators being connected to inputs of a multiplexer whose output is 
connected to the remainder of the circuits of the station, and the control 
inputs of the multiplexer being connected to the output of means for 
detecting a defect on one of the transmission lines so that the latter 
control the multiplexer so that it selects the output of one of the 
comparators as a function of the state of the information transmission 
lines. 
Advantageously, the output of the defect detecting means is connected to 
storage means and/or the means indicating a defect on one of the 
transmission lines.

As can be seen in this drawing, the connection interface according to the 
invention comprises filtering means 1 of known type, the input terminals 
of which are connected to information transmission lines 2 and 3 whereby 
it is possible to connect an information receiving part of a station, 
connected to the output of the interface, to a differential information 
transmission system through two lines for example installed in an 
automobile vehicle. 
The filtering means 1 are also connected to the output of a bias amplifier 
4 delivering a bias voltage to the filtering means. 
The lines 2 and 3, after passage in the filtering means, are respectively 
connected to the non-inverting and inverting inputs of a first comparator 
5 whose output is connected to an input terminal, designated by the 
reference A, of a multiplexer 6 whose output, S is connected to the 
remainder of the circuits of the receiver part of the station. 
The transmission line 2, at the output of the filtering means 1, is also 
connected to a non-inverting input of a second comparator 7 whose other 
input, i.e. the inverting input, is connected to the output of the bias 
amplifier 4 so as to be brought to the bias potential delivered by the 
latter. 
The output of this second comparator 7 is also directly connected to an 
input B of the multiplexer 6. 
The transmission line 3 is connected to an inverting input of a third 
comparator 8, whose other input, i.e. the non-inverting input, is 
connected to the output of the bias amplifier 4. The output of the third 
comparator 8 is directly connected to an input C of the multiplexing means 
6. The multiplexer also has control inputs D and E which are connected to 
the output of means 9 for detecting a defect on one of the transmission 
lines. These defect detecting means deliver a binary word controlling the 
multiplexer so that the latter selects the output of one of the 
comparators as a function of the state of the transmission lines 2 and 3 
so as to obtain an undisturbed output signal, as will be described in more 
detail hereinafter. 
The output of the detecting means 9 may also be connected to storage means 
and/or means for indicating a defect on one of the transmission lines so 
as to permit a diagnostic in real time or in deferred time of the 
information transmission device of the vehicle. These means will be 
described in more detail hereinafter. 
The control inputs D and E of the multiplexer are each connected to the 
output of OR gates 10 and 11 respectively whose inputs are connected to 
flip-flops 12-15 and 18-21 connected in cascade and receiving signals from 
the different comparators. 
Thus for example, with reference to the flip-flops 12-15 connected to the 
inputs of the OR gate 10 whose output is connected to the control terminal 
D of the multiplexer, it can be seen that each input of this gate is 
connected to two flip-flops connected in cascade, respectively 12 and 13 
for the first input, and 14 and 15 for the second input of this gate. 
These flip-flops are for example constituted by flip-flops of type D. 
The flip-flop 12 receives, on one of its inputs, a logic level 1 and its 
output is connected to the input of the flip-flop 13 whose output is 
connected to one of the inputs of the OR gate 10. The driving inputs of 
these flip-flops receive the output signal of the second comparator 7 
while the resetting inputs of these flip-flops receive the output signal 
of an inverter 16 whose input is connected to the output of the third 
comparator 8. 
The driving inputs of the flip-flops 14 and 15 are connected to the output 
of an inverter 17 whose input is connected to the output of the second 
comparator 7, while the resetting inputs of these flip-flops 14 and 15 are 
connected to the output of the third comparator 8. The input of the 
flip-flop 14 is connected to a logic level 1, its output being connected 
to the input of the flip-flop 15 whose output is connected to the other 
input of the OR gate 10. 
It can therefore be seen that these two pairs of flip-flops connected in 
parallel operate with inverted signals derived from the output signals of 
the comparators 7 and 8. 
The control input E of the multiplexer 6 is connected to the output of an 
OR gate 11 whose inputs are also connected to two pairs of D flip-flops 
connected in cascade and carrying the reference characters 18, 19 and 20, 
21 respectively. These pairs of flip-flops are also connected in parallel 
to the inputs of the OR gate 11. 
The driving inputs of the flip-flops 18 and 19 are connected to the output 
of the inverter 16, while the resetting inputs of these flip-flops are 
directly connected to the the output of the second comparator 7. 
The driving inputs of the flip-flops 20 and 21 are directly connected to 
the output of the third comparator 8, while the resetting inputs of these 
flip-flops are connected to the output of the inverter 17. The other 
inputs of the flip-flops 18 and 20 are connected to a logic level 1, their 
outputs being connected to the inputs of the flip-flops 19 and 21 whose 
outputs are connected to the inputs of the OR gate 11. It will also be 
understood that the pairs of flip-flops 18, 19 and 20, 21 respectively 
operate with inverted signals derived from the output signals of the 
comparators 7 and 8. 
The defect detecting means 9 therefore comprise four pairs of two 
flip-flops arranged in cascade and connected in parallel in pairs, each 
pair receiving driving signals and resetting signals which are inverted 
relative to those received by the corresponding flip-flop of the 
associated pair. 
Thus it appears that the operation of such a circuit permits the detection 
of a failure on one or the other of the transmission lines 2 or 3, in that 
the driving signals of the flip-flops are constituted by (direct or 
inverted) signals on one of the lines, while the resetting signals of 
these flip-flops are constituted by (direct or inverted) signals on the 
other line. 
Inasmuch as the device operates in a normal manner, i.e. in a differential 
manner, there are therefore found on the lines 2 and 3 two signals which 
are inverted with respect to each other. The signals circulating on one of 
the lines serve to drive one of the flip-flops, while signals circulating 
on the other line serve to reset the flip-flops. 
In the event of a defect in the transmission on either of the transmission 
lines, the corresponding flip-flops are not reset and there is therefore 
found at the output of the concerned pairs of flip-flops a logic level 1 
which is also at the output of the flip-flop 10 or 11, i.e. at F1 or F2, 
these outputs being connected to the control inputs D and E of the 
multiplexer 6 for the purpose of causing the latter to select the output 
of one of the comparators as a function of the state of the transmission 
lines. 
The following table illustrates the various possibilities of the interface 
according to the invention. 
______________________________________ 
F1=0 F2=0 no defect 
.fwdarw. 
the result of the first 
D=0 E=0 comparator 5 is at the 
output of the multiplexer 
F1=0 F2=1 defect on 
.fwdarw. 
the result of the third 
line 2 comparator 8 is at the 
D=0 E=1 output of the multiplexer 
F1=1 F2=0 defect on 
.fwdarw. 
the result of the second 
line 3 comparator 7 is at the 
D=1 E=0 output of the multiplexer 
______________________________________ 
Thus it can be seen from this table that when two inverted signals 
circulate on the lines 2 and 3, they are mutually neutralized so that at 
the output of the flip-flops 10 and 11 there is a binary word 00, this 
binary word driving the multiplexer so that the latter connects its input 
terminal A to its output S so as to deliver at the output to the rest of 
the circuits of the station the output signal of the comparator 5. 
On the other hand, in the event of a defect on the line 2, the output F2 of 
the gate 11 changes to 1. And the binary word 01 is therefore applied to 
the inputs D, E of the multiplexer 6 so that the latter connects its input 
C to its output so as to select the output of the third comparator 8. 
In the event of a defect on line 3, the output Fl or the gate 10 charges to 
1 and the binary word 1 O is applied to the controlling inputs D, E of the 
multiplexer so that the latter connects its input B to its output and thus 
selects the output of the second comparator 7. 
The signals present at the output of comparators 7 and 8 represent the 
signals circulating on the lines 2 and 3 respectively, it being impossible 
to disturb these signals by possible defects on the other line owing to 
the separation of the analysis thereof in the two different comparators 
driven by a bias voltage. 
In order to facilitate the diagnosis and the repairs of the transmission 
device of the vehicle when the latter has defects, defect indicating means 
22 may also be connected to the output of the defect detecting means 9. 
These defect indicating means 22 may comprise two lights 23 and 24 
connected in the collector circuits of the transistors 25, 26 whose bases 
are respectively connected to the output F1 of the OR gate 10 and to the 
output F2 of the OR gate 11. 
These lights indicate the existence of a defect on either of the 
transmission lines, for example to a user of the vehicle or to a person in 
charge of its maintenance. It will be understood that these indicating 
means may be replaced by defect storing means, it being possible to read 
these storing means by suitable diagnosis equipment.