JPS6367144B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reading engine rotation speed data from a data holding RAM, and in particular to a method for reading and writing simultaneous access when accessing one data to the RAM is divided into two or more cycles. It is an attempt to ban the

Equipment that electronically controls automobile engines, etc.
For example, an electronic carburetor that controls the intake air amount of an engine needs to accurately detect the engine rotational speed to perform control. The engine rotation speed is calculated, for example, by measuring the time interval of several pulses generated per engine rotation.
In a control device using a microcomputer, the interrupt caused by the pulse is used to obtain engine rotation speed data (for example, the above-mentioned time interval),
This is temporarily stored in the data holding RAM and used.

In this case, for example, if the microcomputer is an 8-bit (1 byte) machine and the data handled is 16 bits (2 bytes) or more, the data storage RAM will need to be accessed two or more times for each piece of data. . For example, if one data is 2 bytes, reading or writing is performed in two accesses. For this reason, if the read and write timings coincide, non-existent data that has been partially updated will be read, so it is not preferable to use this for control. Therefore, conventionally, as shown in Figure 1a, the lower byte data A ₁ and the upper byte data
After reading _B1 , the lower data _A2 is read again and it is determined whether it matches the first lower data _A1 . In this way, when A ₁ =A ₂ , it can be determined that B ₁ is a pair with A ₁ .
Furthermore, if A ₁ ≠ A ₂ , there is a possibility that B ₁ has changed during that time, so the data is not used and reading is repeated until A ₁ =A ₂ . However, in this method, as shown in b, since data writing is prioritized by interrupts, there is a drawback that read cycles are wasted. Moreover, since it includes steps for rereading lower-order data and determining whether A ₁ =A ₂ , the control program becomes complicated, and it also has the drawback of requiring a RAM area for A ₂ .

The present invention prevents the above-mentioned simultaneous accesses by simply using a 1-bit flag, and makes it possible to read accurate engine speed data with a simple program.

The present invention provides an engine rotation speed reading method in which engine rotation speed data is written to a data holding RAM and then read out in multiple accesses, and a flag for read priority is provided, and while the flag indicates reading, writing to the RAM is not performed. This will be explained in detail below with reference to the drawings.

FIGS. 2 and 3 are diagrams showing one embodiment of the present invention. In this example, a read priority flag F is provided as shown in FIG.
Set to 1 to prohibit writing. Then, when the reading is finished, the flag F is returned to 0, making it possible to write. The flowchart in FIG. 2 shows this, where a indicates the time of reading and b indicates the time of writing. FIG. 3 shows an example of a control system, where 1 is a data holding RAM, 2 is a CPU (central processing unit), 3 is a time counter, and P is a pulse whose time interval T changes according to the engine speed. The time counter 3 counts the interval T of the pulse P, and the CPU 2 saves the value to the RAM by an interrupt.
Trying to write to 1. During this time, CPU2 is RAM
Since the rotation speed data (in this case, time interval) is read out appropriately from 1 and controlled,
When attempting to write new data to RAM1, refer to flag F to confirm that reading is not in progress (F=1). If reading is not in progress (F=0), the contents of RAM1 are updated in two cycles, but if reading is in progress, it waits.

As described above, according to the present invention, the engine rotational speed data only needs to be read out once, so the number of processing steps is small and there is an advantage that no extra RAM area is required.

[Brief explanation of drawings]

FIG. 1 is a flowchart of a conventional engine speed reading method, and FIGS. 2 and 3 are a flowchart and a block diagram showing an embodiment of the present invention. In the figure, 1 is a data holding RAM, 2 is a CPU, and F is a flag.

Claims (1)

[Claims] 1. In an engine rotation speed reading method in which engine rotation speed data is written to and read from the data holding RAM in multiple accesses, a read priority flag is provided, and writing to the RAM is prohibited while the flag indicates reading. An engine speed reading method that is characterized by: