JPS63236136A - Input filter - Google Patents

Abstract

PURPOSE:To open the filtering time of an input filter consisting of the software to other processes by using an edge interruption routine and a timer coincident interruption routine together. CONSTITUTION:A coincident timer is started by the edge interruption of an input signal to cancel the input change if the signal level has a change within a fixed time and to prescribe the filtering time if the signal level has no change respectively. An edge interruption routine ends after setting a time-out point of said coincident timer. While a timer coincident interruption routine is started when the time-out point of the coincident timer elapses to cancel the input change if the signal level has a change and to perform an input accepting process for the end if the signal level has no change. Thus the filtering time can be utilized for other processes. In other words, a processor is kept free from the filter processing until the timer coincident interruption routine which prescribes the filtering time via the edge interruption routine is started. Thus the processor can perform other processes like a control process, etc.

Description

[Detailed Description of the Invention] [Summary] By using the edge interrupt routine and the timer match interrupt routine together, the filtering time of the input filter by software is released for other processing.

[Industrial application field]

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

[Conventional technology]

A vehicle speed sensor signal whose pulse width changes depending on the vehicle speed is easily affected by mechanical vibrations, ignition pulses, and the like. For this reason, it is common practice to pass this type of signal through a filter before processing it.

FIG. 2 shows a conventional example in which an input filter is configured by software. This input filter is configured as an edge interrupt routine for the vehicle speed sensor signal. Processing ■ compares the signal level taken into the register by the edge interrupt with the subsequent signal level, and if the two are the same, it is determined that there is no noise or chattering (N), and if they are different, it is determined that these are present ( Y). If it is determined that there is (Y), it will be processed ◎
The input change is canceled (the contents of the register are cleared). For example, in the case of an input as shown in FIG. 3, when an interrupt is generated at the first edge E1, the same signal level is maintained until edge E2 appears, so the process branches to N. However, when edge E2 appears, process (2) branches to Y and is temporarily terminated, and an interrupt is generated again at the next edge E3.

After repeating this process and adding v1 to the last edge En, a certain filter time (for example l
m s ), the process (2) branches to Y, and the contents of the register are transferred to the memory in the process (2).

[Problem that the invention seeks to solve]

In the above-described filtering process, the process ``■■'' is repeated until the filter time elapses, so color processing cannot be performed during this time. Generally, in a system that handles vehicle speed sensor signals, vehicle speed control, shift control, etc. are positioned as the main processes, so if the time occupied by input filter processing is long, these main controls will be delayed. Furthermore, with this method, it is not possible to process multiple sensor inputs simultaneously.

The present invention attempts to solve these problems by using edge interrupts and timer match interrupts together.

[Means for solving problems]

The present invention is activated by an edge interrupt of an input signal, and if there is a level change in the signal within a certain period of time, the input change is canceled, and if not, the timeout time of the coincidence timer that defines the filter time is set and the process ends. edge interrupt routine, and a timer match interrupt routine that is activated when the timeout time of the match timer has elapsed, cancels the input change if there is a level change in the signal, or otherwise performs input acceptance processing and ends. The filter time can be used for other processing.

[Effect]

In the present invention, once the edge interrupt routine starts a match timer that defines the filter time, the processor is released from filtering until the timer match interrupt routine is started. Therefore, the processor can perform other processing such as control during this time. It is also possible to simultaneously capture and filter multiple sensor inputs.

〔Example〕

FIG. 1 is a flowchart showing one embodiment of the present invention.
al indicates an edge interrupt routine, and tb> indicates a timer match interrupt routine. Both routines have a process (■), but unlike in Fig. 2, this is a level comparison that is performed only once after an edge interrupt, and generally several to 20 μsl &
This is a level comparison. If it is determined that there is noise or chattering (Y), the input change is canceled in the process ⊚ as in FIG. 2.

In the edge interrupt routine of (a), if it is determined that there is no noise or chattering (N), a timeout time that defines the filter time is set in the coincidence timer in process (2), and the process ends.

The processor is then released from this filtering process.

When the filter time has elapsed and a timer match interrupt occurs, the processor executes the routine (b). Here too, if it is determined that there is no noise or chattering (N), the input reception process (2) is executed and the process ends.

When the edge interrupt routine and the timer match interrupt routine are used together in this way, the loop that repeats the process shown in Figure 2 becomes unnecessary, so the processor can perform other processing after completing the routine in Figure 1 [a]. can move to. Furthermore, when performing multiple sensor input processes, each interrupt process time is short, so similar filtering processes can be performed without affecting each other. Furthermore, in the example of FIG. 3, the filter time can be set earlier than the last edge En, for example, if the time between edges E+ and E2 is longer than the determination time (for example, 20 μs) in process (2), the filter time can be set from the stage of the first edge E1.

〔Effect of the invention〕

As described above, according to the present invention, when an input filter for removing noise and chattering from an input signal is configured by software, a level check is not performed during the filter time, so the processor can perform other processing during that time. Therefore, there are no problems such as other control delays caused by the same processor, and multiple sensor inputs can be taken in and filtered at the same time.

[Brief explanation 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. Applicant Fujitsu Ten Ltd. Representative Patent Attorney Minoru Aoyagi (α) Eng.
(b) Timer match writing if diagram TS2 diagram

Claims (1)

[Claims] An edge interrupt routine that is started by an edge interrupt of an input signal, and if there is a level change in the signal within a certain period of time, cancels the input change, otherwise sets the timeout time of the match timer that defines the filter time and ends. and a timer match interrupt routine that is activated when the timeout time of the match timer has elapsed, and cancels the input change if there is a level change of the signal, otherwise performs input acceptance processing and ends, and the filter An input filter characterized in that time is made available for other processing.