JPH0661109B2 - One-chip microcomputer capable of writing to built-in EPROM - Google Patents

Description

Description: (a) Technical Field of the Invention The present invention relates to a normally 4-bit (4-bit data) one-chip microcomputer mainly used for consumer use such as a microwave oven and an air conditioner, and particularly has an EPROM built-in. The one-chip microcomputer.

(B) Background of the Technology In recent years, it has been desired to combine a RAM or EPROM capable of writing and rewriting data contents with a microcomputer. In a so-called general-purpose microcomputer of 8 bits or 16 bits, the internal or external thereof is required. In addition to the RAM or EPROM, a dedicated address pin is provided for accessing these.

However, generally, in a 4-bit one-chip microcomputer, a mask ROM is usually incorporated as a ROM, and the program content of the ROM is not written after manufacturing. No address pin or data pin is provided for accessing the memory inside the device from the outside.

(C) Prior Art and Problems FIG. 1 schematically shows an example of the overall configuration of a conventional 4-bit one-chip microcomputer, and its constituent elements are a CPU 1, a program counter (PC) 2,
RAM 3, mask ROM 4, decoder 5, input / output ports (I / O ports) 61, 62, 63, 64, 65, 66, ... Are shown. In this type of one-chip microcomputer, for example, a total of 48 input / output pins are provided, but in the illustrated example, four input / output pins P ₁ , P ₂ are provided for each I / O port 61, 62, .... , P ₃ , P ₄ ; P ₅ ,
_{P 6, P 7, P 8} ; ...... is provided.

The CPU 1, the RAM 3, the mask ROM 4 and the I / O ports 61, 62, ... Are connected by a data bus. As described above, each I / O port 61, 62 ,. Output pins P ₁ , P ₂ , P ₃ , P ₄ ; P ₅ ,
P ₆ , P ₇ , P ₈ ; ... Are connected. And CPU1
Address signal for designating an I / O port is input to the decoder 5, a specific I / O port is designated by the output signal of the decoder 5, and data is input / output through the I / O port. An address signal for accessing the mask ROM 4 is input from the output side of the program counter 2 to the mask ROM 4 through the address bus.

In this way, an address bus derived from the output side of the program counter for accessing the built-in mask ROM or an address bus for designating a specific I / O port is provided inside the one-chip microcomputer. However, none of them ends inside the device and is not led out to the outside of the device. Therefore, this kind of one-chip microcomputer has an address port or address pin for connecting these address buses to the outside. I do not have. In the figure, Pi is a reset signal pin for supplying a reset signal to the CPU.

By the way, since the ROM incorporated in the above-mentioned one-chip microcomputer is a so-called mask ROM, its data contents cannot be freely written after manufacturing,
In this respect, even in this kind of one-chip microcomputer, the EPR in which the data contents can be freely written after manufacturing
It may be desired to combine the OMs, in which case it is desirable to have the EPROM built into the device to save mounting area.

However, if such EPROM is built in, in addition to the input / output pins originally possessed by the one-chip microcomputer, address pins and data pins necessary for writing data contents to the EPROM from the outside of the device are further added, the number of pins is increased. However, there is a problem in that the size of the device is increased and a circuit for that is also required, which is uneconomical and the device is enlarged.

(D) Object of the Invention An object of the present invention is to provide a one-chip microcomputer containing an EPROM from outside the device.
When writing the data contents to the EPROM, some of the input / output pins originally possessed by the microcomputer are replaced by the EPROM.
Based on the idea that address pins and data pins for addressing and inputting data to both are also used, the output of the program counter is not derived externally, that is, even if it is a one-chip microcomputer that does not have address pins, EPR built in with the number of pins of the microcomputer kept at the original number
The purpose is to obtain a one-chip microcomputer in a format capable of writing data contents to the OM.

(E) Configuration of the Invention According to the present invention, an EPROM connected to a CPU, data input to and output from the CPU, and the EPRO.
A data bus to which data output from M is supplied; a write bus having a bus line corresponding to the number of write data and address designation for the EPROM; and a data bus connected to the data bus and the write bus, CP
And input / output data to / from U, write data and address to / from an input / output pin, and an input / output port provided from the input / output pin, wherein the input / output port includes the input / output pin and the data bus. And at least one of a first input buffer or an output buffer connected to the input buffer and a second input buffer connected to the input / output pin and the write bus.
At the time of writing to the ROM, the first input buffer and the output buffer are disconnected from the input / output pin and the second input buffer is input / output in response to a control signal instructing the writing to the EPROM. Connect to the pin,
At least one of the first input buffer and the output buffer is connected to the input / output pin and the second input buffer is disconnected from the input / output pin except when writing to the EPROM. Built-in EPROM
Provided is a one-chip microcomputer capable of writing to.

(F) Embodiment FIG. 2 schematically shows the entire configuration of a one-chip microcomputer as an embodiment of the present invention.

The present invention differs from the conventional example shown in FIG. 1 in that
First, in the conventional example, the mask ROM 4 is incorporated as a ROM, but in the present invention, this is replaced with the EPROM 7.

Then, for writing to the EPROM 7, for example, 16 input / output pins among the input / output pins (for example, 48 input / output pins) originally possessed by the one-chip microcomputer
P ₁ , P ₂ , P ₃ , P ₄ , ..., That is, in the embodiment of FIG. 2, input / output ports (I / O ports) 61, 62, 63 and
EPs for a total of 16 pins, each of which has four pins on 64
A writing circuit for ROM is added.

FIG. 3 shows an example of the internal configuration of the I / O port 61 of the one-chip microcomputer shown in FIG. 2. The four input / output pins attached to the I / O port 61 are shown in FIG. P ₁ , P ₂ , P ₃ and P ₄ are inverters 612, 614, 616 and 618 as output buffers, respectively.
Is connected to the data bus, that is, the data input / output circuit via the
The EPROM write circuit is also connected to one end of the EPROM write bus via 611, 613, 615, and 617. The other end of the EPROM writing bus is connected to the EPROM.

Pi is an enable signal input pin for inputting the enable signal _N to each inverter of the EPROM write circuit. In this embodiment, the reset signal pin Pi shown in FIG. 1 is used as the enable signal input pin. Is also used. When a predetermined enable signal _N is input from the pin Pi, the inverters 611, 6
13, 615 and 617 are connected to each other, and EP from the outside of the device through the respective data input / output pins P ₁ , P ₂ , P ₃ and P ₄
In addition to being able to write to the ROM, the inverters 612, 614, 616 and 618 are in a disconnected state, disconnecting the data input / output circuit from the corresponding data input / output pin.

When the required writing to the EPROM is completed, the input of the enable signal is cut off, and conversely the inverter 6
11, 613, 615 and 617 are in the disconnected state, while
Since the inverters 612, 614, 616 and 618 are connected, the EPROM write circuit is disabled and the data input / output circuit is connected to each data input / output pin for normal use.

In addition, in the above-mentioned embodiment, EPRO is used for a total of 16 pins.
An M write circuit is added, but 12 of these pins function as address pins that specify a predetermined address when writing data to the EPROM, and the remaining 4 pins store 4-bit data. Functions as a pin for writing.

Further, in the I / O port 61 shown in FIG. 3, only the output port is shown, but when this is used as a bidirectional input / output port, as shown in FIG. An inverter 6121 as an output buffer for outputting data to the outside and an inverter 6122 as a first input buffer for inputting data from the outside are provided between the data input / output pin P ₁ .

When writing to EPROM, inverters 6121 and 6122
Are disabled to enable only inverter 611 as the second input buffer. Further, during normal use, the inverter 611 is disabled and one of the inverters 6121 and 6122 is enabled according to the input / output of data.

As described above, the present invention is characterized in that some of the data input / output pins originally possessed by the one-chip microcomputer also serve as these pins. In the present invention, it is preferable that the pin Pi for inputting the enable signal is also used as the pin originally possessed by the microcomputer. In the above-mentioned embodiment, the pin for reset is used as the pin Pi, but other than that. It is also possible to use pins for control signals for the above-mentioned applications.

(G) Effects of the Invention According to the present invention, even if the output of the program counter is not derived to the outside, that is, even in a one-chip microcomputer having no address pin, the number of pins of the microcomputer is limited to the original number. It is possible to obtain a one-chip microcomputer in a format that enables high-speed writing of data contents to the built-in EPROM as it is.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing the overall configuration of a conventional one-chip microcomputer, FIG. 2 is a diagram schematically showing the overall configuration of a one-chip microcomputer as an embodiment of the present invention, and FIG. 4 and 4 are diagrams showing an example of the internal structure of the I / O port in the one-chip microcomputer shown in FIG. (Explanation of symbols) 1 ... CPU, 2 ... Program counter, 3 ... RAM, 4 ... ROM, 5 ... Decoder, 61, 62, 63, 64, 65, 66 ... I / O port, 7 ...... EPROM.

Claims (1)

[Claims] 1. An EPROM connected to a CPU, data input to and output from the CPU, and the EPRO.
A data bus to which the data output from M is supplied; a write bus having write data for the EPROM and a bus line corresponding to the number for addressing; and a data bus connected to the data bus and the write bus, CP
And input / output data to / from U, write data and address to / from an input / output pin, and an input / output port provided from the input / output pin, wherein the input / output port includes the input / output pin and the data bus. And at least one of a first input buffer or an output buffer connected to the input buffer and a second input buffer connected to the input / output pin and the write bus.
At the time of writing to the ROM, the first input buffer and the output buffer are disconnected from the input / output pin and the second input buffer is input / output in response to a control signal instructing the writing to the EPROM. Connect to the pin,
At least one of the first input buffer and the output buffer is connected to the input / output pin and the second input buffer is disconnected from the input / output pin except when writing to the EPROM. Built-in EPROM
A one-chip microcomputer that can write to.