Electrical computers and digital data processing systems: input/ – Intrasystem connection – Bus interface architecture
Reexamination Certificate
2000-08-14
2002-04-02
Myers, Paul R. (Department: 2181)
Electrical computers and digital data processing systems: input/
Intrasystem connection
Bus interface architecture
C375S220000
Reexamination Certificate
active
06366976
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention generally relates to a device for connecting a subscriber to a bus line. In addition, the invention relates to a circuit for determining the transmission direction of such a device for connecting a subscriber to a bus line.
Various generally known possibilities for connecting subscribers to a bus line
1
are represented in FIG.
2
. In the example shown, data are transmitted on the bus line
1
with differential signals. For this purpose, the bus line
1
possesses two signal cores B and A, on which the data are represented in voltage-level-coded form, and a shielding C to shield the line against interference. An example of a voltage-level-coded embodiment, is the RS 485 interface, in which a voltage differential between the cores B and A greater than 0.2 V is interpreted as the digital value “1” and a voltage differential of less than −0.2 V is interpreted as the digital value “0.” The transmission of data is bi-directional, that is, data can be transmitted in both directions. The subscribers
2
and
5
are disposed at opposite ends of the bus line
1
. Since the length of the bus line
1
can be several hundred meters, a termination for the suppression of interfering reflections at the end of the line is provided in the subscribers
2
and
5
. This termination can, for example, include a 390 &OHgr; resistor between a 5 V power supply and the signal core B, a 220 &OHgr; resistor between the signal core B and the signal core A, and a 390 &OHgr; resistor between the signal core A and the ground. This termination corresponds essentially to the characteristic wave impedance of the bus line
1
. The termination in each of the subscribers
2
and
5
is marked by a T in a rectangular box. By thus dimensioning the termination resistors, the idle state or resting state on the bus
1
, i.e., the voltage differential, resulting from highly ohmic outputs of the subscribers
2
. . .
5
, is determined to be about 1 V. At the inputs of the subscribers, this idle state is interpreted as the digital value “1.” The bus line
1
is looped through a subscriber
4
, which is located somewhere between the two ends, without noteworthy changes of the characteristic wave impedance. Thus, no termination is required for this subscriber. A subscriber
3
is connected to the bus line
1
by a branch line
6
. This arrangement is preferred, for example, when a subscriber is not located in the immediate vicinity of the bus line and if it is difficult, due e.g. to the stiffness of the bus line, to run the bus line to the subscriber. At a data rate of up to 1.5 MBaud, a length “a” of the branch line
6
should be at most 1.5 m, since the branching point at the connection point of the branch line
6
to the bus line
1
causes a disturbance of the characteristic wave impedance and reflections. These reflections arise at the subscriber
3
, which is connected, without termination, to the branch line
6
. The reflections run back, via the branch line
6
, into the bus line
1
, and interfere with the data transmission. A subscriber connection of this type thus reduces the transmission reliability of a bus system.
OBJECTS OF THE INVENTION
It is one object of the invention to provide a device with which a subscriber is easily connected to a bus line even if the subscriber is not located in the immediate vicinity of the bus line. It is a further, related object to provide such a device whereby the transmission reliability of the bus system is not significantly worsened by the connection of the subscriber.
Normally, a connection device of this type would require a signal for controlling the data transmission direction. However, subscribers, which are designed for bi-directional transmission of data, in general do not provide such a signal on their bus interface, since it is not needed in the normal case when the subscriber is connected directly to its bus interface on the bus system. Accordingly, it is a further object of the invention to provide a circuit for determining the transmission direction in the connection device. Yet another object of the invention is to provide such a circuit that can be set up cost-effectively and with ease.
SUMMARY OF THE INVENTION
These and other objects of the invention are achieved by a device to connect a subscriber to a bus line for bi-directional data transmission as well as by a transmission direction detection circuit for such a device. According to one formulation of the invention, the device includes a branch line to connect the subscriber with the device. The device furthermore includes an amplifier circuit to selectively transmit signals from the bus line to the branch line and from the branch line to the bus line. The amplifier circuit has a high-resistance input at the bus line and has outputs, which are switched between an active operation mode and an inactive operation mode. In the active operation mode, a respective connected one of the bus line and the branch line is driven by the signals received by a respective other one of the branch line and the bus line. In the inactive operation mode, at least one of the outputs has a high resistance.
The device also includes a direction determination circuit to detect if the signals are to be transmitted from the bus line to the branch line or from the branch line to the bus line, and to activate a respective one of the outputs.
According to another formulation of the invention, the transmission direction determination circuit includes a branch line connection to connect the subscriber to the transmission direction detection circuit. The transmission direction detection circuit also includes an amplifier circuit transmitting signals from the bus line to the branch line. Therein, the data transmission on the branch line is digitally voltage-level-coded with predetermined response thresholds to detect digital values. Furthermore, the transmission direction detection circuit includes a first resistor network and a first buffer generating a first determination signal. The first resistor network corresponds substantially to a star connection and includes a first series resistor and a second series resistor. The first resistor is arranged between a first star point of the star connection and an input of the first buffer. The second series resistor is arranged between the first star point and the at least one output of the amplifier circuit. Therein, the at least one output is located on a side of the branch line of the amplifier circuit. In addition, the first resistor network includes a connection of the first star point with the branch line and clamp resistors at the input of the first buffer and at the branch line against power supply voltages.
The first series resistor, the second series resistor, and the first clamp resistors are dimensioned such that a first change of a voltage level (which is supplied from the at least one output of the amplifier circuit to the first resistor network and which corresponds to a change of at least one of the digital values) changes the voltage level on the branch line such that the change of the at least one digital value is detected at a connected input of the subscriber. Therein, the first change of the level changes the level at the input of the first buffer only slightly so that the change of the at least one digital value is not detected at the first buffer.
Furthermore, the first series resistor, the second series resistor, and the first clamp resistors are dimensioned such that a second change of the voltage level (which is supplied from the branch line to the first resistor network and which corresponds to the change of the at least one digital value) changes the level at the input of the first buffer such that the change of the digital value is detected by the first buffer.
It is one advantage of the invention that a subscriber is connected to the bus line via a branch line, wherein the quality of the signals on the bus line is not worsened. With a device according to the invention, if necessary, longer branch lines and/o
Myers Paul R.
Siemens Aktiengesellschaft
LandOfFree
Device for connecting a subscriber to a bus line does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device for connecting a subscriber to a bus line, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for connecting a subscriber to a bus line will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2932820