JPH0621990B2 - Input filter - Google Patents

Description

DETAILED DESCRIPTION [Overview] By using an edge interrupt routine (means) and a timer coincidence interrupt routine (means) together, the filter time of an input filter by software is released to other processing.

[Industrial application field]

The present invention relates to an input filter that softly removes noise and chattering from an input signal.

[Conventional technology]

The vehicle speed sensor signal whose pulse width changes according to the vehicle speed is easily affected by mechanical vibration, ignition pulse, and the like. For this reason, it is common to filter such signals before processing them.

FIG. 2 shows a conventional example in which such an input filter is configured by software. This input filter is configured as an edge interruption routine of the vehicle speed sensor signal. The processing compares the signal level taken into the register by the edge interrupt with the subsequent signal level. If they are the same, it is judged that there is no noise or chattering (N), and if they are different, they are present (Y ). If it is determined to be present (Y), the input change is canceled in the process (the contents of the register are cleared). For example, in the case of the input as shown in FIG. 3, if the interrupt is applied at the first edge E ₁ , the same signal level is maintained until the edge E ₂ appears, so the process branches to N. However, when the edge E ₂ appears, the process branches to Y and ends once, and an interrupt occurs again at the next edge E ₃ . When such a process is repeated and an interrupt occurs at the last edge En, the process branches to Y after a lapse of a certain filter time (for example, 1 ms), and the content of the register is transferred to the memory in the process.

[Problems to be solved by the invention]

In the above-described filter processing, the processing is repeated until the filter time elapses, and therefore other processing cannot be performed during this time. Generally, in a system that handles a vehicle speed sensor signal, vehicle speed control, speed change control, and the like are positioned as the main processing, so that a long occupation time of the input filter processing causes a delay in the main control. Further, such a method cannot process a plurality of sensor inputs at the same time.

The present invention intends to solve these problems by using both edge interrupt and timer coincident interrupt.

[Means for solving problems]

The first aspect of the present invention is to determine whether there is a change in the level of an input signal.
And an edge interrupt routine including the step of terminating the processing by setting the timeout time of the coincidence timer that defines the filter time if there is no change in the level of the input signal in the first determination step. A second determination step of determining whether or not there is a signal level change;
If there is no change in the level of the input signal in the second judgment step, input acceptance processing is performed, and if there is a level change, a timer coincidence interrupt routine having a step of canceling the input change and terminating, The edge interrupt routine is activated by a level change, and after the routine is activated, execution of the edge interrupt routine thereafter is prohibited until the time-out time elapses, and when the time-out time elapses, the timer interrupt routine And a processing means for activating.

[Action]

In the present invention, after the match timer that defines the filter time is started by the edge interrupt routine, the processor is released from this filtering process until the timer match interrupt routine is activated thereafter. Therefore, the processor can execute processing such as control during this time. Also, multiple sensor inputs can be simultaneously captured and filtered.

〔Example〕

FIG. 1 is a flow chart showing an embodiment of the present invention.
(a) shows an edge interrupt routine, and (b) shows a timer match interrupt routine. Both routines have processing, but unlike FIG. 2, this is a level comparison that is performed only once after an edge interrupt, and is generally a level comparison several to 20 μs after the interrupt. There is noise or chattering here (Y)
If it is determined that the input change is canceled by the process similar to FIG.

In the edge interrupt routine of (a), when it is determined that there is no noise or chattering (N), the process sets the timeout time for defining the filter time in the coincidence timer and ends. The processor is then freed from this filtering. Eventually, if the filter time elapses and a timer match interrupt occurs,
The processor executes the retin in (b). In this case as well, the input reception process is executed when it is determined that there is no noise or chattering (N), and the process ends.

When the edge interrupt routine and the timer coincidence interrupt routine are used together in this way, the loop for repeating the process as shown in FIG. 2 becomes unnecessary, so the processor shifts to another process after the routine of FIG. 1 (a) ends. You can Further, when a plurality of sensor input processes are performed, the respective interrupt process times are short, so that similar filter processes can be performed without affecting each other. Further, in the example of FIG. 3, at a time earlier than the last edge En, for example, the edges E ₁ and E ₂
If the interval is longer than the processing determination time (for example, 20 μs), the filter time can be set from the stage of the first edge E ₁ .

〔The invention's effect〕

As described above, according to the present invention, when the input filter that removes noise and chattering from the input signal is configured by software, the level is not checked at the filter time, so the processor can perform other processing during that time. . Therefore, there is no other problem such as control delay due to the same processor, and a plurality of sensor inputs can be simultaneously taken in and filtered.

[Brief description of drawings]

 FIG. 1 is a flowchart showing an embodiment of the present invention, FIG. 2 is a flowchart of a conventional vehicle speed input filter, and FIG. 3 is a waveform diagram of a vehicle speed sensor signal.

Claims (1)

[Claims] 1. A first determination step of determining whether or not there is a level change of an input signal, and a time-out time of a coincidence timer that defines a filter time if the level of the input signal does not change in the first determination step. An edge interrupt routine including a step of terminating the processing, a second determination step of determining whether the level of the input signal has changed, and an input if the level of the input signal does not change in the second determination step. A timer coincidence interrupt routine including a step of performing acceptance processing and canceling and ending the input change if there is a level change, and the edge interrupt routine is activated by the level change of the input signal, and after the routine is activated , The execution of the edge interrupt routine thereafter is prohibited until the time-out time elapses, and before the time-out time elapses. Input filter comprising the processing means for starting a timer interrupt routine.