JPH0965456A - Voltage level conversion circuit for multiplex communication path for automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain voltage conversion in an accurate timing by inhibiting the reception of a communication path of an opposite party so that the output signal of a voltage level conversion circuit connecting to communication paths with different voltage levels is not returned to an original reception signal side. SOLUTION: A CPU 101 of an engine controller 100 uses an I/O 103 to diagnose sensors and actuators and receives an instruction signal from a tester 201 to provide the output of count and diagnosis results. A voltage level conversion circuit 110 is provided between communication paths of different voltage levels, and a reception inhibit circuit 113 stops signal reception and start of a communication path occupancy time timer 116 while a signal from the opposite party stays on the communication paths and a reception permission circuit 114 inhibits a signal output while its own signal stays on the communication paths. Thus, the reception of its own transmission signal is avoided and complicated software processing for signal discrimination is not required and the processing is simplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication path for reading out data indicating an operating state of a microcomputer, and more particularly to a microcomputer circuit having different voltage levels.

[0002]

2. Description of the Related Art In order to detect the operating state of a microcomputer, a method of monitoring data corresponding to a predetermined address on a data bus of the microcomputer has been conventionally used. However, due to the one-chip microcomputer, there are many configurations in which the data bus is not output to the outside, which makes it difficult to detect the operating state.
As an example of such a monitor device, there is JP-A-58-107998.

Therefore, the monitor is limited to a specific address,
Means have been taken to monitor the data by serial signals. Since the transmission signal and the reception signal are separated from each other in the serial signal, there is a problem that only one monitor device can correspond to one microcomputer as it is.

Therefore, a method has conventionally been used in which a transmission signal and a reception signal are multiplexed and serial signals of a plurality of microcomputers are communicated through a single communication path.

[0005]

FIG. 1 shows a connection for communication between a plurality of microcomputers by multiplexing, and it is premised that serial signals of all microcomputer circuits operate at the same voltage level. I am trying.

Therefore, it cannot be connected to a microcomputer circuit having a different signal level. For example, 0 and V
At the signal level where B (12V) is the logic level,
There is a threshold at about 50%. As shown in FIG. 2, when connected to a circuit in which 0 and Vcc (5V) are signal levels, even if 5V is output as a high level, 50% of VB is output.
Since it is (6V) or less, it is received as a low level and communication is not established.

An object of the present invention is to provide a means for connecting communication paths of such different voltage levels and signal levels.

[0008]

As shown in FIG. 3, while one microcomputer circuit is outputting a serial signal, the output signal is prioritized and the communication path of the other side is prohibited. To do. In this state, the voltage of the output circuit is converted so that the signal level is adjusted to the other side.

[0009]

[Operation] By prohibiting the reception of the communication path on the other side,
The voltage converting circuit does not return the voltage-converted output signal to the original reception signal side, so that the voltage conversion can be performed at accurate timing.

[0010]

FIG. 4 shows an embodiment of the present invention.

The engine control device 100 has a microcomputer 101 and a serial interface SCI 102 for outputting the operating state. The signal on the communication path is connected to the reception signal RX through a comparator that determines high and low levels at a predetermined threshold value. The TX signal is connected to the transistor through the inverter and is connected to the communication path with the open collector.

The microcomputer 101 is used for automobile engine control, and uses the I / O 103 to perform self-diagnosis of input sensors, switches, and output actuators. Also, the number of pulses corresponding to the rotation of the crankshaft of the engine is counted to measure the engine speed.

The diagnostic result and the count value are stored in the RAM in the microcomputer, and by receiving a specific command signal from the tester 201, the operating state such as the count value and the diagnostic result is output to the outside.

A voltage level conversion circuit 110 is provided between the communication paths from the microcomputer circuits to convert the voltage.

The voltage conversion circuit includes a reception circuit 111, a signal delay circuit 112, a reception prohibition circuit 113, and a reception permission circuit 11.
4, an output circuit 115, and a communication path occupation time timer 116.

The receiving circuit determines high and low with a threshold value according to the voltage level of the communication path. The signal delay circuit compensates for the delay time in which the reception prohibition circuit is in the prohibition state in order to prevent the serial signal of the other side from being received around.

The reception prohibition circuit stops signal reception and activation of the communication channel occupation time timer while the other party's serial signal is on the communication channel.

The reception permission circuit permits signal output while its own serial signal is on the communication path.

The output circuit connects the output of the reception permission circuit with the open collector to the communication path of the other party.

The communication path occupation time timer is a one-shot that outputs a signal indicating the time from the start bit to the stop bit of the serial signal, and its inverted output prohibits reception on the other side.

The serial signal is a start bit and data 8
It consists of bits and stop bits, and sends out 1 byte of data within 10 bits from the fall of the start bit. The stop bit sends high level at the end of data transmission. Therefore, the microcomputer circuit occupies the communication path for 10 bits. 1
Since the 0th bit is high, it is only necessary to prohibit reception on the other side for 9 bits or more and less than 10 bits.

Therefore, by prohibiting the receiving side from receiving while the communication path is occupied, it is possible to prevent the transmission output 1 from returning to the output circuit 2 through the receiving circuit 2.

For example, when the baud rate is 7812 bps, 1 bit is 125 μs, so 1125 μs
One shot from (9 bits) to less than 1250 μs (10 bits).

The tester is GST, a self-diagnosis device for automobiles.
In the case of (Generic Scan Tool), it is 10410 bps, and the mask time of 864 μs to 960 μs is set.

In FIG. 5, the receiving circuit is the inverter 10 with hysteresis, and the signal delay circuit delays about 2 μs by the CR integrating circuit.

The reception prohibition circuit is AND11, and reception is prohibited while the inverted output of the one-shot 02 is low.

The reception enable circuit is AND12, and reception is possible while the output of the one shot 01 is high.

The output circuit is a transistor, and AND12
The output is inverted and the open collector is connected to the voltage level Vcc or VB of the other side through a resistor in the communication path.

The communication occupation time timer is set to one shot 01, and a pulse of a predetermined width is output from the first rising edge of the reception prohibition circuit output. The inverted output is the reception prohibition circuit A on the other side.
Connected to ND21 to inhibit reception on the other side while the pulse is low.

Inverter 20, AND2 having the same configuration
1, the AND 22, the one-shot 02, and the output circuit 32 constitute a voltage conversion circuit.

With these configurations, when a signal is transmitted from the engine control device to the tester 201 as shown in FIG.
Since the one-shot 01 generates a pulse and prohibits the reception of the AND 21, the output circuit transistor 32 is kept in the off state, and the communication signal to the tester does not return to the engine control device.

On the contrary, when the tester outputs a signal first, the engine control unit also prohibits reception.

[0033]

INDUSTRIAL APPLICABILITY The present invention can be used to prevent reception of a transmission signal by multiplexing a serial signal.

Conventionally, since the transmitted signal is returned to the receiving terminal as it is, complicated software processing is performed as a means for discriminating between the signal from the external communication path and the own signal. That is, processing such as time measurement from the transmission interrupt to the reception interrupt and comparison between the transmission data and the reception data are performed.

However, as shown in FIG. 7, if the one-shot pulse is generated at the trailing edge of the transmission signal and the reception signal is masked during the low level, the transmission signal is not received. Therefore, there is no need to perform complicated software processing, and there is an effect of simplifying the processing.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a conventional problem.

FIG. 2 is an explanatory diagram of conventional problems.

FIG. 3 is an explanatory diagram of the principle of the present invention.

FIG. 4 is a block diagram of an embodiment of the present invention.

FIG. 5 is a block diagram of a second embodiment of the present invention.

FIG. 6 is a timing chart of the present invention.

FIG. 7 is a block diagram of a third embodiment of the present invention.

[Explanation of symbols]

100 ... Engine control device, 101 ... Microcomputer, 102 ... SCI, 103 ... I / O, 110 ... Voltage level conversion circuit, 111 ... Reception circuit, 112 ... Signal delay circuit, 113 ... Reception prohibition circuit, 114 ... Reception permission circuit ,
115 ... Output circuit, 116 ... Communication channel occupation time timer, 2
01 ... Tester.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H04L 25/02 H03K 19/00 101A

Claims (1)

[Claims] 1. A sensor for detecting an operating state of an internal combustion engine,
An actuator for controlling the controlled variable based on the operating state, a microcomputer circuit having a self-diagnosis means according to the operating state, a communication circuit for outputting the operating state and the self-diagnosis result to the outside using a serial communication circuit, A voltage level of a multiplex communication path for an automobile, comprising: a multiplex communication path for an automobile that simultaneously performs a plurality of communications; and a voltage conversion circuit for connecting communication paths having different signal voltage levels of the multiplex communication path. Conversion circuit.