JP2003304295A - Transmission circuit for communication signal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmission circuit for a communication signal in which a transmission state is surely detected and signal transmission is surely performed even if microcomputers or signal converters by different makers or of different types are used. <P>SOLUTION: The transmission circuit comprises: three signal lines, of a signal ground line, S.G, an A side signal line, and a B side signal line; a plurality of computer means sending and receiving data signals: and a plurality of signal converters connected to each of the plurality of computer means through the signal lines. Each of the computer means detects the start and termination of data by finding that the data signals retain the H level for a specified period of time or longer to fetch the data. Each of the signal converters compares the voltage level of the A side signal line with that of the B side signal line to determine the H or L level of the data sent to the receiving side terminal of each of the computers. The A side signal line and the B side signal line apply resistance division to voltage between the H level and the L level and are always biased so that a potential difference may arise at a voltage in the intermediate range of the H level and the L level and between the A side signal line and the B side signal line. <P>COPYRIGHT: (C)2004,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal transmission for communication between computer devices via a signal ground line and a total of three signal lines A and B. Related to the circuit. 2. Description of the Related Art Hitherto, a signal transmission circuit in the above-mentioned communication has been configured as shown in FIG. In the figure, A,
The three lines B and SG are signal lines for communication, SG is a signal ground line, and A and B are voltage signal lines, on which signal voltages are transmitted so that the data signals to be transmitted have opposite phases. R is a resistor connected between the signal lines AB. A signal converter 1 and a signal converter 2 are connected to the signal line, and a microcomputer 1 and a microcomputer 2 are connected to the signal converter, respectively. Between each microcomputer and the signal converter,
Transmission signal terminal TX, signal transmission status output terminal TX ENA
BLE, error receiving terminal ERROR, signal receiving terminal RX
Connected. FIG. 4 shows a flow chart for transmitting a signal from the microcomputer 1 to the microcomputer 2 in the circuit shown in FIG. In FIG. 4, a is a data signal transmitted from the TX of the microcomputer 1 to the signal converter 1, and H indicates a state without communication.
As the level, signals are sequentially transmitted with the first L level as a start bit, and the process ends with the last H level. At the same time, the signal EN indicating that the microcomputer 1 is in the transmission state is sent from the TX ENABLE terminal of the microcomputer 1 to the signal converter while the H level continues for a time covering the start bit to the end bit. The signal converter 1 sends the signal of c to the terminal A and the signal of d to the terminal B from the signal TX and the signal TX ENABLE to the signal line. The signal converter 2 receives the aforementioned signals c and d, and sends the signal e to the RX of the microcomputer 2. At this time, the signal transmission device 2 determines the H level and the L level of the signal transmitted to the RX by comparing the voltage on the A side with the voltage on the B side. For example, in FIG. 4, when both AB are L, L, A
When the voltage on the A side is higher than the B side, that is, when A is H and B is L, H is applied. When the voltage on the A side is lower than the B side, ie, when A is L and B is H, the L Output to RX. The microcomputer 2 determines that a transmission signal has arrived when the RX terminal signal continues to be at the H level during the time t1 of the RX terminal signal as indicated by d, and receives a signal from the first L level to the time t2 thereafter, as data. If the H level continues, it is determined that transmission of the transmission signal has ended. The data signal a is transferred from the microcomputer 1 to the microcomputer 2 as described above. [0005] However, in the above description, the microcomputer 1 and the microcomputer 2 are the same series of the same maker, and the TX ENABLE of the microcomputer 1 is used for t1 and t3 determined by the microcomputer 2. There is no problem if the signals match, but the situation is different when the transmitting side is from the personal computer of FIG. 3 having a different type of microcomputer or a signal converter of another manufacturer and the signal converter 3. FIG. 5 shows a signal flow corresponding to FIG. 4 in such a case. In FIG. 5, a is a signal transmitted from the personal computer, b is a signal at the terminal A of the signal converter 3, c is a signal at the terminal B, and d is a signal at the RX terminal of the microcomputer 2. Normally, there is no ENABLE signal in a transmission signal from a personal computer, and only a data signal is output. The signal converter 3 is forced to enter the signal transmission state before the data signal t2 '.
1 ′ H-level signal and t to end the signal transmission state
An H level signal of 3 'is added and output from the A terminal, and the signal is transmitted to the RX terminal of the microcomputer 2. However, depending on the type and the manufacturer of the signal converter 3, the signal of the microcomputer 2 is used. T1 'and t3' for the judgment times t1 and t3
Is too short to detect that the microcomputer 2 is in a signal transmission state, that is, the signal transmission may not be performed properly. SUMMARY OF THE INVENTION It is an object of the present invention to provide a communication signal transmission circuit that can reliably detect a transmission state and perform signal transmission reliably even when using microcomputers and signal converters of different manufacturers and types. And SUMMARY OF THE INVENTION Accordingly, the present invention relates to a signal ground line SG, three signal lines A and B, and a plurality of computers for transmitting and receiving data signals. Means, and a plurality of signal converters connected to each other through a signal line for each of the plurality of computer means, wherein the computer means determines whether the data signal is at H level for a predetermined time or more. The signal converter compares the voltage levels of the A-side signal line and the B-side signal line to detect the H level of the data to be transmitted to the receiving terminal of the computer device. In determining the L level, the A-side signal line and the B-side signal line
The communication signal is characterized in that a voltage between the L level and the L level is divided by a resistor, and a voltage in an intermediate range between the H level and the L level is constantly biased so that a potential difference occurs between the A-side signal line and the B-side signal line. A transmission circuit is provided. An embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 illustrates an embodiment of a signal transmission circuit according to the present invention. In the figure, signal lines A, B, SG, signal converter 2, signal converter 3, microcomputer 2, personal computer, and R
Are the same as in FIG. 3, and the description is omitted. R1 is the signal line A
And the resistor connected between the H voltage (+ 5V) and the signal line B
And a resistor connected between the L voltage (0 V). FIG. 2 illustrates the flow of a signal for transmitting a data signal from the personal computer of FIG. FIG. 2A shows a transmission data signal from the personal computer. B in FIG.
And c are signal waveforms at the A and B terminals of the signal converter 3 in FIG. In FIG. 2, the H level is + 5V and the L level is 0V. T1 'and t3' shown in FIG. 2B are signals added by the signal converter 3 to indicate the start and end of the signal transmission state described in FIG. A terminal and B terminal of the signal converter 3 are H (+ 5V) or L when the signal is being transmitted.
(0 V), and is in an open state (a state where it is not connected to a signal line) when it is not in a signal transmission state. Therefore, in the signal transmission state from t1 'to t3' in FIG. 2, the signal lines A and B repeat either the state of +5 V or 0 V by the signal converter 3,
At times other than the signal transmission state deviating from the time of 1 ′ to t3 ′, the potential difference (5V) between both ends of the series resistance of R1, R, and R2.
Are divided voltages. That is, the voltage of the signal line A becomes (5 × (R + R2) / (R1 + R + R2)) V,
The voltage of the signal line B is (5 × R2 / (R1 + R + R
2)) Divided to V. Therefore, when the signal is not in the transmission state, the voltage of the signal line A is always higher than the voltage of the signal line B. The signal lines A, B, SG in such a state
The signal converter 2 connected to the microcomputer always outputs a signal of H to the microcomputer 2 during the time outside the time t3 'from the time t1' because the voltage of the terminal A is higher than the voltage of the terminal B. To the RX terminal of the microcomputer 2. In this case, the microcomputer 2 determines that the signal transmission state continues irrespective of the time of t1 'and t3', so that the transmission data from the personal computer can be reliably received. As described above, according to the present invention, even if a microcomputer or a signal converter of a different manufacturer or model is used, a communication signal capable of reliably detecting a transmission state and reliably transmitting a signal can be obtained. Can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram of an embodiment of a communication signal transmission circuit according to the present invention; FIG. 2 is a diagram of a signal waveform at each position of signal transmission in the embodiment of FIG. 1; FIG. 4 is a diagram of a signal transmission circuit at each position of signal transmission between the microcomputer 1 and the microcomputer 2 of FIG. 3 FIG. 5 is a diagram of a signal waveform at each position of signal transmission between the personal computer and the microcomputer 2 of FIG. Diagram of signal waveforms [Description of symbols] A: Signal line A side B: Signal line B side SG: Signal ground line side R1, R, R2 ... Resistance

Claims (1)

Claims: 1. A signal ground line SG, three signal lines of an A-side signal line and a B-side signal line, a plurality of computer means for transmitting and receiving data signals, and each of the plurality of computer means. And a plurality of signal converters connected to the signal line via a signal line. The computer means detects the start and end of the data by detecting that the data signal has been kept at the H level for a predetermined time or more. The signal converter compares the voltage levels of the A-side signal line and the B-side signal line, and outputs H or L of the data to be transmitted to the receiving terminal of the computer device.
In determining the level, the A-side signal line and the B-side signal line are divided in voltage between the H level and the L level by resistance, and are in the range between the H level and the L level. A communication signal transmission circuit, which is always biased so that a potential difference is generated in the communication signal.