JPH036944A - Control bus line collision prevention device - Google Patents

Abstract

PURPOSE:To prevent the collision of a bus line and to detect signal collision in a short time by setting a comparison reference threshold level higher than a conventional threshold level while sending a start signal prior to a control data and resending a signal according to the predetermined priority. CONSTITUTION:When a control signal is sent from only one control means 12, a start signal is sent to set a comparison reference threshold level 16 to a level V2. Then the comparison reference threshold level 16 is compared with the level of a bus line to monitor the collision of the bus line. When the two control means 12, 22 start the transmission of a control signal entirely simultaneously, the level of the bus line goes to a level E1 and the level E1 is nearly a multiple of 1.8 of the level E0. Since the comparison reference threshold levels 16, 26 are set to the level V2, the occurrence of the collision is recognized. Waiting times T1, T2 depending on the priority of the devices 1, 2 are set to T=T1, T=T2 to reset a timer (t). The collision is avoided by varying the length of the waiting times T1, T2 depending on each device.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a collision prevention device for a control bus line communication system that operates with multiple masters.

BACKGROUND OF THE INVENTION In recent years, control bus line communication systems have been widely used for the purpose of simplifying communication lines for controlling multiple devices.
Furthermore, in order to simplify communication procedures, so-called multi-master bus line communication systems have begun to be used, which allow control signals to be transmitted from any device connected to the bus line. In such a multi-master bus line communication system, control signals can be transmitted from any device, so in some cases control signals may collide on the bus line, so it is necessary to provide a means to prevent such collisions. .

A conventional control bus line collision prevention device will be described below.

FIG. 4 shows the configuration of this conventional control bus line collision prevention device, and FIG. 5 shows signal waveforms of the conventional control bus line collision prevention device.

In FIG. 4, l is the first
equipment, 2 is the bus line! a second device connected to 0;
11. 21 is a terminating resistor that prevents reflections on the communication line; 12;
22 is a control means for controlling bus communication; 13. 23 is a voltage amplifier; 14. 24 is a diode that separates the voltage amplifier 13.23 and bus line 0 when the control means is outputting "L"; 15.25 is a comparator for detecting the bus line control signal; 18.28 is the comparator 15 The comparison reference threshold is .degree.25.

The operation of the control bus line collision prevention device configured as above will be described below.

First, a case will be described in which a control signal is transmitted from only one control means. For example, the control signal transmitted only from the control means 12 belonging to the first device 1 is transmitted to the voltage amplifier 13.
．． The bus line 10 is driven through the diode 14. The control signal of the bus line is detected by the comparator 25 belonging to the second device 2 by comparing it with the comparison reference threshold 26, and its output is input to the control means 22. The signal is detected by the bus line, and is also input to the control means 12, which monitors the control signal of the bus line. Conversely, even when a control signal is transmitted only from the control means 22 belonging to the device 2, the control signal is similarly input to the control means 12 and the control means 22.

FIG. 5 shows the signal waveform of this conventional example. In FIG. 5, the line between a and b is a start signal transmitted prior to control data, the line between b and c is a start bit for bit synchronization of control data, and the line after point c is control data. The control means 12 to which the control signal is to be transmitted has the bus line set to “L”.
After confirming that this is the case, first a start signal is transmitted to set the bus line to "H", and then a start bit and control data are transmitted. As soon as the control means 22 confirms that the bus line has become "H", it enters the receiving state.

Next, a case will be described in which control signals are transmitted from two control means at the same time. If start signals are sent from two control means at the same time, a bus line collision will occur.
In this case, the following arbitration is performed to determine the priority device. While each control means is transmitting a control signal, it constantly checks the logic of the transmission data it transmitted and the data on the bus line, and if the logic is reversed, the device loses the arbitration and immediately stops transmitting. Stop and change to the receiving side.

FIG. 5 shows an example of how arbitration is performed. In FIG. 5, control means 12. 22 transmits the start signal at the same time at point a, then up to point g the control means 12. 2
2 have exactly the same output, so the logic of the data sent by itself and the data on the bus line match and collision detection is not performed, but the control means 12 outputs "H" between g and b. , since the control means 22 outputs "L", the signal on the bus line IO becomes "H" due to the effect of the diode 24, and the control means 22 outputs the transmission data "L" sent by itself.
It detects that the logic of the data "H" on the bus line is inverted, immediately stops transmitting the control signal, and changes to the receiving side.

On the other hand, since the data transmitted by the control means I2 and the data on the bus line match, the control means I2 continues transmission. In this way, when a bus line conflict occurs and arbitration is performed, “H
The device transmitting "" is given priority, and the control data is not destroyed and bus line collisions can be prevented.

Problems to be Solved by the Invention However, in the above-described conventional configuration, it is unclear which device will be given priority in arbitration when there is a signal collision on the bus line. In addition, each device must constantly monitor the bus line control signals to detect signal collisions when transmitting control signals.
Moreover, each control means has the problem of having to store the control signal of the bus line up to the point in time when the signal collision of the lotus line is detected so that it can respond to the change of control means to the receiving side at any time.

The present invention solves the above-mentioned conventional problems. It is possible to detect a signal collision in a short time, there is no need to store control signals up to the time of signal collision detection, and it is possible to set priorities for each device when a signal collision occurs on a bus line. The purpose of the present invention is to provide a bus line collision prevention device that can be attached to a bus line.

Means for Solving the Problems The present invention is a multi-master control bus line collision prevention device in which a plurality of devices are connected to a bus line, wherein each device connected to the bus line transmits a signal to the bus line. current-driven bus line driving means for outputting a signal on the bus line; bus signal detection means for detecting a signal on the bus line and having a comparator for comparing the signal on the bus line with a first or second threshold value; outputting a signal to the driving means and receiving a signal from the bus signal detecting means, and when a signal exceeding a second threshold is detected, a predetermined retransmission time after a different retransmission time determined by priority for each device; and control means for transmitting a time-continuous start signal, and the first. The second threshold value is set to a lower level and a higher level, respectively, than the level when a start signal is applied to the bus line from one device.

Effects The present invention has the above-described configuration. (1) While the control means transmits the start signal prior to the control data, the comparison reference threshold of the bus signal detection means is set to a second threshold higher than the normal value. I am trying to detect line signal collisions.

(2) When signal collision on the bus line is detected, signals are retransmitted according to predetermined priorities, thereby preventing signal collision on the bus line.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of a control bus line collision prevention device in an embodiment of the present invention, FIG. 2 is a signal waveform diagram of the bus line collision prevention device in an embodiment of the present invention, and FIG. 3 shows an implementation of the present invention. It is a flowchart of the bus line collision prevention device in an example.

In FIG. 1, l is the first
2 is a second device connected to the bus line IO,
11. 21 is a terminating resistor that prevents reflections on the communication line; 12;
22 is a control means for controlling bus communication; 13. 23 is a voltage amplifier; 14. 24 is the control means 12. 22
voltage amplifier 13. is transmitting "L". 23 and the diode separating the bus line lO, Is, 25
is a comparator for detecting the control signal of the bus line, I
G, 2G is comparator 15. 25 comparison reference thresholds, 17. 27 is a resistor for driving the bus line with current, and its resistance value is equal to the terminal resistor 11.27 of the bus line.
The value is set to be larger than 21, for example, 5 times larger than 21.

The operation of the control bus line collision prevention device of this embodiment configured as described above will be described below.

As shown in FIG. 2, the potential of the bus line when one of the control means transmits "H" is EO1, and the potential of the bus line when two control means transmit "H" at the same time is El. EO and El are resistors 11 and 21. 17.
27, and in this embodiment, the voltage amplifier 1
3. The output of 23 is E, and the voltage drop of the diode is e.
In this case, from the circuit diagram in Figure 1, EO = 1/11 (E
-e), El=1/6-(E-e). Therefore, El
is approximately 1.8 times that of EO. Also, comparator 15.
25 comparison reference threshold IG, 211i is the control means 12
．． 22 is V2 when transmitting a start signal, and V when not transmitting a start signal, O<V+<Eo, Eo<V2
<El.

The operation will be explained below according to the flowchart shown in FIG. In step 2, T=O is set. In step 3, timer t is reset. In step 4, each control means 12.
22 is the comparison reference threshold 1[i
, 2G are set to V, and in step 5, the potential of the bus line IO and the comparison reference threshold are compared. In step 5, if the potential of the bus line IO is "L" compared to the comparison reference threshold V, the process proceeds to step 6, and the presence or absence of a transmission request is checked.

If there is no transmission request, return to step 4 and step 4. 5. Repeat the routine 6. In step 5, if the potential of the bus line 10 is "H" compared to the comparison reference threshold V, the process proceeds to the reception routine 12. If there is a transmission request in step 6, the process proceeds to the next series of transmission procedures.

Next, a case where a control signal is transmitted from only one control means 12 will be explained. If there is a transmission request in step 6 during the above-mentioned standby, the process proceeds to step 7, where the magnitude of t and T is determined. Now, since T=0, the process advances to step 8 and a start signal is transmitted. Thereafter, in step 9, the comparison reference threshold 16 is set to V2. In step 10, the bus line potential is compared with the comparison reference threshold 111i to monitor bus line collisions. In this case, since only one control means 12 is transmitting the start signal, the potential of the bus line is EO.
The potential EO of the bus line is V of the comparison reference threshold lG.
Since it is "L" compared to 2, the transmission routine of step 13 is entered, and the start bit and control data are transmitted following the start signal.

On the other hand, the other control means 22 enters the receiving routine in step 12 since the potential of the bus line becomes "H" higher than the comparison reference threshold value V+ of 26 in step 5.

Similarly, when the control signal is transmitted only from the control means 22, the control means 22 proceeds to the transmission routine, and the control means 12
enters the receive routine.

Next, two control means 12. 22 start transmitting control signals at exactly the same time. In this case, as mentioned above, the potential of the bus line becomes El, and El is approximately 1 of EO.
．． It becomes 8 times. Up to step 9, the operation is similar to that described above, but in step 9, the comparison reference threshold IEi, 2ft is v2.
Therefore, in step 10, it is detected that the potential of the bus line is "H" compared to the comparison reference threshold value V2 of 18.26, and it is determined that a collision has occurred. If it is found that a collision has occurred on the bus line, in step 11 the waiting times T I, T 2 are determined according to the priority of each device 1.2, so that T = T1. T
= T*, and return to step 3, and continue in step 4. 5. 6. Repeat routine 7. Collisions can be avoided by varying the lengths of these waiting times TI and T2 for each device. For example, the control means I2 is
2, the waiting time TI of the control means 12 is set to be smaller than the waiting time T2 of the control means 22. As shown in FIG. 2, a collision is detected when a start signal is transmitted between a and b, and the control means 12. The control means 22 then proceeds to step 11. At point 0, which is T1 seconds after point b, t>TI, the control means 12 proceeds to step 8, and retransmits the start signal. At the time when the control means I2 retransmits the start signal, the control means 22 performs step 4 described above since TI<T2. 5. 6. However, in step 5, the potential of the bus line reaches the comparison reference threshold V.
It is detected that the signal has become "H" compared to 1, and the reception routine is entered. Therefore, even at point d 12 seconds later, the start signal is not retransmitted. Therefore, collisions are avoided, and the control means 12 receives the start bit according to the predetermined priority order.

Send control data.

As described above, according to this embodiment, by varying the comparison reference threshold of the bus signal detection means, the bus line is monitored only when the start signal is transmitted, and the storage of the bus line signal before collision detection is unnecessary. I can do something. Further, by varying the time until retransmission of the control signal in the event of a bus line collision according to the priority order, it is possible to prioritize each device in the event of a bus line signal collision.

Effects of the Invention According to the present invention having such features, the bus line can be monitored only when the start signal is transmitted, and the storage of bus line signals before collision detection can be made unnecessary. It is possible to prioritize each device in the event of signal collision on the line, which has great practical effects.

[Brief explanation of drawings]

FIG. 1 shows a configuration diagram of a control bus line collision prevention device according to an embodiment of the present invention, FIG. 2 is a signal waveform diagram of the control bus line collision prevention device according to an embodiment of the present invention, and FIG. It is a flowchart of the control bus line collision prevention device in an example, and is a signal waveform diagram of the collision prevention device. l...first device, 2...second device, II,
21...Terminal resistor, 12. 22...control means, 13. 23...voltage amplifier, 15. 25・
... Comparator, IEi, 2G... Comparison standard threshold,
17.27...Resistance.

Claims (1)

[Claims] A multi-master control bus line collision prevention device in which a plurality of devices are connected to a bus line, wherein each device connected to the bus line is driven by a current that outputs a signal to the bus line. bus line driving means; bus signal detection means having a comparator for comparing the signal on the bus line with a first or second threshold and detecting the signal on the bus line; A start signal that continues for a predetermined period of time after different retransmission times determined by priority for each device when a signal exceeding a second threshold is detected while outputting a signal from the bus signal detection means. and control means for transmitting a signal, and the first and second threshold values of the bus signal detection means are lower and higher than the level when a start signal is applied to the bus line from one device. A control bus line collision prevention device characterized in that each of the control bus line collision prevention devices is set to .