JPS58214951A - Time counting system using free running counter - Google Patents

Abstract

PURPOSE:To simplify the device constitution, by actuating a free running counter at all times during application of an electric power supply to obtain the difference of value between the start and end time points of counting and detecting the borrows and overflows during operation of the counter to discriminate the effectiveness of the obtained value. CONSTITUTION:A free running counter 1 is always actuated during application of a power supply, and the time interval is obtained from the difference between the value S of the starting time point and the value E of the finishing time point of counting. With such a system, the 1st flay 4 showing the presence or absence of a borrow during calculation is set together with the 2nd flag 3 showing the overflow frequency during the counting. Then the calculated time interval data is decided effect only in case the absence is discrimiated for both the overflow and borrow from the flags 4 and 3 and also in case the presence is discriminated for the overflow of once and a borrow. This eliminates a comparing register and simplifies the device constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a timekeeping system using a free-running rotor.

A microcomputer has a free-run counter that starts when the power is turned on, and is used to measure, for example, the time from one interrupt to the next. When the time interval to be measured is limited to a certain range, the number of bits of the free run counter is usually set so that it can measure within that range. Within this range, at the start of measurement (S
The time interval T can be determined by calculating the difference between the time data T1 at ) and the time data T2 at the end of the hand side (E).

T=72−T+ However, time interval data of automotive control equipment,
For example, the reciprocal of the engine rotational speed has a large value before and during engine startup, so even if the above formula is used, the data will be meaningless unless it is detected how many times overflow occurred during that time.

Moreover, this value is considered to be data during high-speed rotation and is used without regard to overflow, which causes an inconvenience.

FIG. 1 is an explanatory diagram of this, where I is a 16-bit free-run counter. Since it is 16 bits, the count value is 0000.
It changes in the range of ~FFFF (hexadecimal), but in the diagram, the left end is 0000 and the right end is FFFF to make the explanation easier to understand.
It's Toshide. It is assumed that a solid line arrow between the measurement start time S and the measurement end time E indicates a time interval T. (
In case A), since the ink hull T is short, the interval T can be easily calculated by simple subtraction T=E-3. (B)
Cases (C) and (C) each overflow, but in both cases the end time E does not exceed the start time S, so if borrow (polarity reversal) is ignored, the time interval can be calculated as <T=E-3.

However, in case (D), T=E-3 becomes a short value similar to (A), and unless a value for one cycle is added to this value, it becomes a significantly inaccurate value.

Conventionally, in such cases, a conveyor register 2 was used as shown in Fig. 2 for the purpose of removing the interval data in case (D) from the viewpoint that it was sufficient to be able to accurately time the cases (A) to (C). ing.

A value E' one count before the measurement start point S is set in this conveyor register 2, and with this as the limit value, if an overflow occurs, T=E- only within the range of E<E'.
3 is made valid, and when E≧E', the data is made invalid. However, in order to do this, 16 bits are required for conveyor register 2, so the RAM
This has the disadvantage that the program becomes more complex because it occupies more space and requires constant comparison.

The present invention attempts to determine the validity of time interval data by simply providing two types of flags regarding overflow and borrow.

The present invention is characterized in that a time interval is calculated from the difference between a value at the start of measurement and a value at the end of measurement using a free-run counter that operates constantly while the power is turned on. A first flag indicating the presence or absence of a borrow and a second flag indicating the number of overflows during the measurement period are set, and if it is determined from these flags that there are no overflows and borrows, and there is one overflow. The calculated time interval data is validated only when it is determined that there is a borrow. This will be explained in detail below with reference to the illustrated embodiment.

FIG. 3 is a schematic diagram showing an embodiment of the present invention. In this example, as shown in Fig. 3, a flag 3 indicating the number of overflows and a flag 4 indicating the presence or absence of a borrow are provided, and when the time interval measurement is started using the counter l, the corresponding items are displayed in these flags 3.4. write (borrow,
The overflow determination function is in a normal microcomputer). Flag 4 is 1 bit, and the presence or absence of a borrow is indicated by 1 or O. On the other hand, flag 3 is a 2-bit flag that indicates the number of overflows: 0, 1, and 2 or more.
Shown by type. The validity of interval data is judged using these flags 3.4 as shown in the table below.

Table 1 In the table above, valid (A) is the case in Figure 1 (A), valid (B,
C) is the case of (B) and (C) in the same figure, and invalidity (D) is the case of (,D) in the same figure. FIG. 4 is a processing flow for determining whether data is valid or invalid according to the above table.

As described above, according to the present invention, it is possible to judge whether data is valid or invalid only by determining the number of counter overflows and the presence or absence of a borrow in the calculation result for measuring the time interval.
This has the advantage that no area is required and constant comparison between the conveyor register and the counter is not required.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of time interval measurement using a free run counter, Figure 2 is an explanatory diagram of the conventional time measurement method, and Figure 3 is an explanatory diagram of time interval measurement using a free run counter.
The figure is a block diagram showing one embodiment of the present invention, and FIG. 4 is a flowchart for determining effectiveness. In the figure, 1 is a free run counter, 3 is a flag indicating the number of overflows, and 4 is a flag indicating the presence or absence of a borrow. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] In a timekeeping method that uses a free-run counter that operates at all times while the power is turned on to calculate the time interval from the difference between the value at the start of measurement and the value at the end of the hand side, the first counter indicates the presence or absence of a borrow at the time of calculation. A flag and a second flag indicating the number of overflows during the needle side period are set, and if it is determined from these flags that there is no overflow or borrow, or it is determined that there is one overflow and a borrow. A timekeeping method using a free-run counter, which is characterized in that calculated time interval data is validated only when the time interval data is calculated.