JPH0475696B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an access method for bus-based networks.

The access method for the bus network is as follows:
CSMA/CD (Carrier Sense Multiple Access/
Collision Detection) method, Token passing method, etc. However, the former method has the disadvantage that the number of collisions increases and throughput decreases under high load, while the latter method has the disadvantage that all tokens are passed regardless of whether there is a transmission request or not. The problem is that as the number of node stations increases, the throughput decreases as the number of node stations increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a bus access system that can immediately avoid contention even if a collision occurs, and that does not increase throughput even when the number of node stations increases.

According to the present invention, in a network in which a plurality of node stations are connected by a bus, a contention field is provided in a signal frame, and when a node station that performs transmission detects a no-signal state on the bus, it starts transmitting and also self-transmits. A signal corresponding to an address or a code assigned to a transmission method is sent in the contention field, and when a sending bit of the signal is level 0, a signal corresponding to a level 1 bit is sent to the bus. A bus-based network access method is provided in which a node station that detects a signal stops transmitting data.

Next, the present invention will be explained in detail with reference to the drawings. Figure 1 shows the configuration of a bus network.
The network shown in FIG. 1 is composed of node stations 2, 3, 4, 5, and 6 connected by a bus 1, and termination devices 7 and 8 that terminate the bus 1.

The access method according to the present invention will be explained using the signal diagram on the bus 1 shown in FIG. Consider the case where node stations 2, 3, and 4 start transmitting simultaneously after detecting the idle state of bus 1. FIG. 2a shows a collision situation in which signal frames from these node stations overlap on bus 1. FIG. 3 shows the structure of the signal frame sent out from each node station. node station 2, 3,
4 sends out a preamble PR, and further sends out a signal CODE corresponding to each address in the competition field shown in the figure. Each node station has a different signal CODE, and the signals CODE of node stations 2, 3, and 4 are 110, 101, and 011, respectively. preamble
Following PR, the node stations 2, 3 and 4 each transmit the first bit of the signal code, ie 1, 1, 0, as shown in FIGS. 2b, c and d. The signal levels on bus 1 in the contention field are shown in FIG. 2e. At the first bit, level 1 signals of node stations 2 and 3 are added, and the level of bus 1 is greater than 1. This signal level is received by all node stations. Node station 4 is level 0
Since the bus 1 is at level 1 or higher even after outputting the first bit of , it gives up on acquiring the transmission right and immediately stops transmission. Therefore, the second and third bits 1, 1,
1 is not sent. Node stations 3 and 4, which sent out the first bit of level 1, continue to send the signal
Sends the second bit of CODE. Even though the node station 3 has sent out the second bit of level 0, a signal of level 1 is supplied to the bus 1, and it enters a non-idle state and stops transmitting the third and subsequent bits of the signal CODE. In the third bit,
Node station 2 outputs level 0, detects that bus 1 is at level 0, recognizes that it has acquired the sole transmission right, and sends out the information frame shown in FIG. Note that the information frame is composed of a start flag SF, destination address DA, originating address SA, information field INFO, and end flag EF.

Next, FIG. 4 shows the configuration of the node station used in this embodiment. The node station in FIG. 4 includes an access control circuit 11 and an idle detection circuit 1.
2, a monostable multivibrator 13, a transmission buffer 14, and a reception buffer 15, all of which are connected to the bus 1. Monostable multivibrator 13 is triggered by the busy state of bus 1 and outputs level 1. The pulse width of the output pulse signal generated by this monostable multivibrator 13 is set to be longer than the time length of the competition field. When a transmission request occurs, the access control circuit 11 sends out a preamble PR based on the fact that the idle detection circuit 12 detects an idle state and the output of the monostable multivibrator 13 is 0. Note that in each node station, when the signal level on bus 1 is 0 in the contention field,
The idle detection circuit 11 apparently determines it to be idle, but this is because the monostable multivibrator 13 is triggered by the preamble PR on the bus 1 and holds output 1 for longer than the time width of the contention field. are distinguished, so that apparent idleness in the contention field does not result in a node station starting a new transmission. The access control circuit 11 of the node station that started the transmission transmits the preamble
At the same time as sending out the signal CODE following PR, the output of the idle detection circuit 12 is monitored, and the signal
If the bus 1 signal level is 1 even though the level 0 bit of CODE has been sent out, the transmission is immediately stopped and the monostable multivibrator 1
Wait until the output of bus 3 becomes 0 and bus 1 becomes idle. From now on, this control is repeated until the signal
The node station that is able to transmit all CODEs acquires the transmission right and transmits the information frame in the transmission buffer 14.

As described above in the case of a collision, if a collision does not occur, bus 1 will not become level 1 when the level 0 bit of the signal CODE is sent, so the accessed node station can continue to transmit data. .

As described above, according to the present invention, even if a collision occurs, the collision state can be resolved within the conflict field.

FIG. 5 shows another example of a signal frame used in the present invention. The contention field of this signal frame is composed of a priority signal PI and a signal CODE. The priority signal PI is given depending on the communication characteristics or the number of times transmission has been stopped due to collision. For example, a higher priority is given to synchronous communication such as voice, or a higher priority is given as the number of transmission stops increases. Note that the length of one bit in the contention field may be greater than the bit width in the information frame. In addition, in a system that performs bit synchronization between each node station by extracting the clock from the signal on bus 1, if the signal frames shown in Figures 3 and 5 are insufficient for synchronization, the contention field and start flag A field for synchronous withdrawal may be provided between SFs.

FIG. 6 shows a signal diagram of the bus 1 at the time of a collision in another embodiment of the present invention, and FIG. 7 shows the configuration of the node station used in this embodiment. The node station of FIG. 7 has a subtraction circuit 16 instead of the idle detection circuit 12 of the node station of FIG.
A driver 17 is further added between the bus 1 and the access control circuit 11.

FIG. 61 shows the time position of each field of the transmitted signal frame. As shown in FIG. 6, the access control circuits 11 of the node stations 2, 3, and 4 that started transmitting at the same time send the first bit of each signal CODE to the bus 1 via the driver 17 following the preamble PR. Send. The subtraction circuits 16 of these node stations remove their own signals supplied to the negative inputs (-) from the signals on the bus 1 supplied to the positive inputs (+), and notify the access control circuit 11 of the presence or absence of a collision. The outputs of the subtraction circuits 16 of the node stations 2, 3, and 4 are shown in FIGS. 3, 5, and 7. The node station 4 stops transmitting since the level of the first bit of the signal CODE is 0, and the output of the subtraction circuit 16 is 1 or more, indicating that the bus 1 is in a non-idle state. Therefore, the signal shown by the broken line in FIG.
The remaining bits of CODE are not transmitted. Node stations 2 and 3 send out signal level 1, but
Since the output of the subtraction circuit 16 is 1, it continues to send out the second bit of the signal CODE. When transmitting the second bit, only the node station 2 transmits a signal level 1. Therefore, as shown in FIGS. 3 and 5, the subtraction circuit 16 of the node station 2
The output of the node station 3 becomes 0, and the output of the subtraction circuit 16 of the node station 3 becomes 1. Therefore, the node station 3 immediately stops transmitting, and the third bit of the signal CODE shown by the broken line in FIG. 4 is not transmitted. Although the node station 2 sent out the signal level 1, since the output of the subtraction circuit 16 is 0, it recognizes that there is no collision and does not send out the third bit of the signal CODE shown by the broken line in FIG. Immediately acquires the transmission right, activates the transmission buffer 14, and transmits the information frame.

In the case of non-collision, the transmitting node station can detect the non-collision state when transmitting the preamble and can immediately acquire the transmission right without transmitting the contention field.

As described above, according to the present invention, even if a collision occurs, one node station can acquire the transmission right without repeating the collision, and each node station can access the token at random. Unlike the bus system, there is no wasted time due to circulation of transmission rights.

Furthermore, priority control is also possible, and synchronous communication can be integrated.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a bus type network.
Figure 2 a, b, c, d, e and Figure 6 1, 2,
3, 4, 5, 6, 7 are signal diagrams on the bus, 3rd
FIG. 5 is a diagram showing a signal frame used in the present invention. FIGS. 4 and 7 are diagrams showing the configuration of a node station used in the present invention. In the figure, 1 is a bus, 2, 3, 4, 5, and 6 are node stations, 7 and 8 are terminal devices, 11 is an access control circuit, 12 is an idle detection circuit, and 1
3 is a monostable multivibrator, 14 is a transmission buffer, 15 is a reception buffer, 16 is a subtraction circuit, and 17 is a driver.

Claims (1)

[Claims] 1. In a network in which multiple node stations are connected by a bus, a contention field is provided in the signal frame, and when a node station that performs transmission detects a no-signal state on the bus, it starts transmitting, and also transmits its own address or Sending a signal corresponding to the code assigned to the message in the contention field;
An access method for a bus type network, characterized in that a node station detecting that a signal corresponding to a level 1 bit is being sent to the bus when the sending bit of the signal is level 0 stops transmission. .