JPH054018Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a circuit that switches the oscillation format of an oscillation circuit built into a microcomputer, etc., and particularly relates to a circuit that switches the oscillation format of an oscillation circuit built into a microcomputer, etc. related to microcomputers, etc.

(B) Prior Art Generally, a 4-bit or 8-bit one-chip microcomputer has a built-in oscillation circuit for creating a system clock for controlling system operations. This oscillation circuit is
The oscillation format can now be changed depending on the purpose of use of the microcomputer.

Figures 2A and 2B are circuit diagrams of the oscillation circuit built into the microcomputer.

Figure 2 A shows an RC that oscillates by connecting a resistor R and a capacitor C to external terminals 1 and 2.
It is an oscillation circuit, and includes a Schmitt inverter 3,
It is composed of a NOR gate 4 and an inverter 5. The other input of NOR gate 4 has a control signal OSC that controls the start and stop of oscillation of the oscillation circuit.
When CONT is applied, oscillation can be stopped and a standby state can be established when a halt instruction is executed. Although this RC oscillation circuit has poor oscillation frequency stability, it can obtain sufficient oscillation output immediately after oscillation starts, and is therefore used when it is desired to operate a microcomputer immediately after releasing the halt state.

On the other hand, FIG. 2B shows a ceramic oscillation circuit that oscillates by connecting a ceramic resonator (or crystal resonator) CF capacitor C to external terminals 6 and 7, and controls the start and stop of oscillation. an inverter 8 controlled by the signal OSC CONT;
Feedback resistor 9 connected between input and output of inverter 8
It consists of This ceramic oscillator circuit is
Although it takes a certain amount of time for the oscillation to stabilize immediately after the start of oscillation, the oscillation frequency is stable and a high oscillation frequency can be obtained, so it is used when operating a microcomputer at high speed.

The circuits in Figure 2 A and B were created on December 25, 1986.
It is described on page 237 of ``'87 Sanyo Semiconductor Data Book, Microcomputer, Memory, Gate Array Edition'' published by CQ Publishing Co., Ltd.

(c) Problems to be solved by the invention However, the selection of the oscillator circuits shown in Figure 2 A and B is based on the mask for manufacturing the semiconductor integrated circuit of the microcomputer after the specifications of the microcomputer have been determined. Therefore, if specifications are changed after manufacturing, the oscillation format of the oscillation circuit cannot be changed. Also,
When changing the oscillation format, the mask itself must be changed, which increases costs associated with changing the mask.

(d) Means for solving the problem The present invention was created in view of the above points, and the oscillation element is provided between two terminals to which the oscillation element is externally connected. an oscillation circuit,
A switch circuit inserted between one of the terminals and each oscillation circuit, a signal holding circuit that outputs a control signal for controlling on and off of the switch circuit, and information for generating the control signal is stored. To provide an oscillation format switching circuit which is equipped with a nonvolatile memory (EP-ROM) having a region and can easily change the oscillation format of an oscillation circuit by rewriting information in a predetermined region of the nonvolatile memory.

(E) Effect According to the above-mentioned means, when "1" is stored in a predetermined area of the nonvolatile memory, "1" is held in the signal holding circuit, and the switch connected to one of the oscillation circuits is The circuit turns on,
The oscillation format of the oscillation circuit is selected. Conversely, when a predetermined area of the nonvolatile memory is changed to "0", "0" is held in the signal holding circuit, and the switch circuit connected to the other oscillation circuit is turned on by the control signal, and that oscillation circuit is turned on. The oscillation format is selected. Therefore, the oscillation format can be freely changed by rewriting the nonvolatile memory.

(F) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention.
10 is an RC oscillation circuit, similar to Fig. 2A,
Schmitt inverter 11, control signal OSC
Consists of a NOR gate 12 to which CONT is applied, an inverter 13, and a Schmidt inverter 11
The input of the inverter 1 is connected to the external terminal 14.
A transmission gate 16, which is a switch circuit, is connected between the output of No. 3 and an external terminal 15.
17 is a ceramic oscillator circuit, which, as in FIG. connected to terminal 14 and inverter 18
A transmission gate 20, which is also a switch circuit, is connected between the output and the external terminal 15.

The control signal OSC CONT controls the start and stop of oscillation of the RC oscillation circuit 10 and the ceramic oscillation circuit 17, and becomes "1" when a halt command is executed, stopping both oscillations and eliminating the halt state. When released, it becomes "0" and oscillation starts. Transmission gate 16,2
0 are both controlled by the control signal RC/CF, but when the control signal RC/CF is "1", only the transmission gate 16 is turned on and the RC
When the oscillation circuit 10 is selected and the control signal RC/CF is “0”, the transmission gate 20
only is turned on, and the ceramic oscillation circuit 17 is selected. The oscillation output is obtained from the output of an inverter 21 whose input is connected to the connection point between the transmission gates 16 and 20 and the external terminal 15, and is supplied to a clock pulse generation circuit (not shown) of the microcomputer.

The EP-ROM 22 is a non-volatile memory built into the microcomputer, into which programs or data can be written electrically from the outside, and which can be erased by ultraviolet light or electrically. . This EP-ROM
In 22, data is written and read by addressing, but in the predetermined area 23, the written data can be taken out separately from the original bus line (not shown) for reading data. The data output line is D-FF2.
It is connected to input D of 4. D-FF24 is a signal holding circuit for the control signal RC-CF, and is controlled by the initial setting signal INT applied to the clock input φ.
Data stored in a predetermined area 23 of the EP-ROM 22 is input and held, and output as a control signal RC/CF.

Therefore, if "1" is written in the predetermined area 23 of the EP-ROM 22, the control signal RC/CF becomes "1" after the initial setting signal INT is generated, and the transmission gate 16 is turned on.
RC oscillation circuit 10 is selected. On the other hand, EP−
If “0” is written in the predetermined area 23 of the ROM 22, after the initial setting signal INT is generated,
The control signal RC/CF becomes "0", the transmission gate 20 is turned on, and the ceramic oscillation circuit 17 is selected.

Therefore, by rewriting the data in the EP-ROM 22 and changing the data stored in the predetermined area 23 based on changes in the specifications of the microcomputer,
The format of the oscillation circuit can be selected.

(g) Effects of the invention As mentioned above, according to the invention, even if the specifications change at any time, the oscillation format of the oscillation circuit can be changed simply by rewriting the EP-ROM, so the user can easily change the oscillation format. This has the effect of providing a microcomputer that is extremely easy to use and useful.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIGS. 2A and 2B are circuit diagrams showing conventional examples. 10...RC oscillation circuit, 17...Ceramic oscillation circuit, 16, 20...Transmission gate, 22...EP-ROM, 24...D-FF.

Claims (1)

[Scope of utility model registration request] A plurality of different types of oscillation circuits are provided between two terminals to which an oscillation element is externally connected, a switch circuit is inserted between one of the terminals and each oscillation circuit, and the switch circuit is turned on. or a signal holding circuit that outputs a control signal for controlling off, and a non-volatile memory (EP-ROM) having an area in which information for generating the control signal is stored, the area of the non-volatile memory An oscillation format switching circuit characterized in that one of the different formats of oscillation circuits is selected based on information stored in the oscillation format switching circuit.