JPS5814626A - Counting device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a counting device, particularly a frequency dividing circuit that divides a first signal having a predetermined repetition frequency to generate a second signal;
The invention relates to a counting device including a counting circuit that accumulates a value and generates a third signal when a second signal is counted up to the accumulated value.

Such a counting device is used as a timer for a microprocessor. For example, a frequency divider circuit is a prescaler that divides the system clock of a microprocessor.
The counting circuit is, for example, a counter that generates a timer interrupt signal. Conventionally, when using such a counting circuit as a timer, a certain value is written to the counter from the data bus,
A counter counts the divided clocks, that is, downgraded clocks, by the prescaler, and when the counted value matches the accumulated value, an interrupt signal is generated. However, since the prescaler is always running based on the system clock, variations occur in the time from when a value is written to the counter until the first branch clock is generated by the prescaler. In other words, when using this counting circuit as a timer, a value corresponding to a desired time is written to the counter, but at the time when a write signal is given to this counter, and when the prescaler counts the system clock up to a predetermined number and divides the clock The time it takes to output one pulse varies within a time range that corresponds to the maximum period of the divided clock. Therefore, this variation may result in an error of several percent with respect to the expected time, that is, the value written to the counter. Therefore, such a conventional counting circuit has the disadvantage that precise time control cannot be performed in a microprocessor.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate such drawbacks of the prior art and provide a counting device that can perform precise time control.

This object can be achieved according to the invention by a counting device comprising means for initializing the branch circuit in response to the accumulation of values in the counting circuit.

According to one SS of the present invention, such initial setting means initializes the frequency dividing circuit in response to a data write signal of the counting circuit of the microprocessor.

Next, embodiments of a counting device according to the present invention will be described in detail with reference to the accompanying drawings.

The figure is a block diagram showing an embodiment of a microprocessor of a counting device according to the present invention. In the figure, a counting device according to the present invention receives a system clock CLK of a microprocessor at a clock terminal 10, counts it, and when a predetermined count value is reached, reads the divided clock 12.
It has a prescaler 14 that generates a clock, and a counter 16 that counts this branch clock. Counter 16 is a circuit that writes or reads binary values from other circuits of the microprocessor through data bus 18, and may be of any type that counts up or down the divided clock on read 12. good. A counter 16 receives a read (R) or write (W) signal from the control (B) path of the microprocessor.
o is connected, which clears the prescaler 14 (cL
R) 11 is also connected to the child 22. The output terminal INT of the counter 16 produces an output on its terminal 24 which can be used by the system as, for example, a timer interrupt signal.

For example, if the prescaler 14 and counter 16 are of a down-count type, the prescaler 14 is initialized to a predetermined value when receiving a signal at the terminal 22, and when the system clock appearing at the terminal 10 is counted up to the predetermined number, the counted value becomes 0. Then, one pulse is generated in the lead 12, and the counting down from the predetermined count value is repeated cyclically. Therefore, a divided clock having a constant period appears on lead 12. Counter 16 stores the digital value received from data bus 18 and opens a gate (not shown) connected to lead 12 and a gate that receives a write signal from lead 20 to read the digital value from the stored count. Start countdown. When the frequency-divided clock on the lead 12 is counted and the counted value becomes O, the counter 16 generates a pulse on the lead 24.

According to the present invention, the write signal on the lead 20 is connected to the clear terminal 22 of the prescaler 14, so that a digital value is written and accumulated in the counter 16 through the data bus 18, and when the write signal appears on the lead 20, At the same time, the prescaler 14 is also initialized to a predetermined value. Therefore, from the time when a write signal appears at terminal 20 from the control circuit of the microprocessor, the prescaler 1
4 or the first pulse of the divided clock appears on lead 12 corresponds to a predetermined value that initializes prescaler 14, and since this value is always constant, counter 16 increases by -5. , the time from receiving a write signal from the control circuit on lead 20 to generating an output signal on lead 24 always corresponds exactly to the value written to counter 16 from data bus 18. Therefore, even if this counting device is used as a time control timer, there will be no variation in the time control.

By configuring the counting device according to the present invention as described above, precise time control without error can be performed. This can be particularly effectively used as a time measurement timer for a microprocessor, making it possible to control time on the order of several microseconds without causing errors.

[Brief explanation of drawings]

The figure is a block diagram showing an embodiment of a microprocessor of a counting device according to the present invention. 14... Prescaler, 16... Counter, 22...
...Initial setting means. Agent Patent Attorney Susuki 1) Toshiyuki

Claims (1)

[Claims] 1. A frequency dividing circuit that divides a first signal having a predetermined repetition frequency to generate a second signal;
a counting circuit that generates a third signal when counting the signals up to the accumulated value, the counting device initializing the frequency dividing circuit in response to the accumulation of the values of the counting circuit. A counting device characterized in that it includes means. 2. II. In the counting device according to claim 1, the first signal is a system clock of a microprocessor, and the initial setting means operates the frequency dividing circuit in response to a data write signal of the counting circuit. A counting device characterized by initializing i.