JPH02310786A - Microcomputer - Google Patents

Abstract

PURPOSE:To enable a program to be written on or read from a memory from the outside by providing a selector in the inside of a microcomputer. CONSTITUTION:When an ordinary mode is designated by a mode signal 17, the selector 5 selects a bus so as to perform the delivery of a signal with an external address/data bus 7 to only a CPU 2, and the selector 16 connects a bus 13 for address control signal for the memory 11 to a bus 15 for address control signal from the CPU 2, and connects a data bus 12 to a data bus 14 from the CPU 2. Also, when a memory access mode is set, the selector 5 separates the external address/data bus 7 from the CPU 2, and connects it to the selector 16, and the selector 16 separates the CPU 2 from the memory 11, and connects a bus 10 for address control signal to the bus 13 for address control signal, and connects a data bus 9 to a data bus 12. In such a way, access from the outside to the memory of the microcomputer 1 can be permitted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a microcomputer, and more particularly to a microcomputer called a single-chip microcomputer that has a built-in nonvolatile read-only memory.

[Conventional technology]

In recent years, with the miniaturization of devices, single-chip microcomputers, which can integrate the necessary memory on the same device and reduce the mounting area, have been increasingly used, especially in small systems such as home appliances.

The type of nonvolatile read-only memory integrated into this single-chip microcomputer also changed from the original mask R.
, evolving from OM, FROM (programmable ROM)
), EPROM (ultraviolet erasable PROM)', EE
Various products have been developed, including PROM (electrically erasable FROM).

Programs are written to these nonvolatile memories, except for mask ROMs, using a dedicated writer called a FROM writer. Even if the microcomputer has a means for sending and receiving data to and from the outside, this writing is configured to be performed independently of the means. Therefore, writing cannot be performed on a system using a microcomputer, and programs cannot be read externally.

When using EEPROM, there are products that allow writing on the system without using a ROM writer, but this is limited to data used by the arithmetic processing section in the microcomputer, and programs cannot be written to it.

[Problem to be solved by the invention]

With the conventional microcomputers mentioned above, it is not possible to write programs on the system that uses the microcomputer, so it is not possible to modify the program on the system, or to transfer programs written in one microcomputer to other programs. The disadvantage is that it cannot be executed by a microcomputer.

Furthermore, recently, the processing speed of internal calculations of microcomputers has improved, and the problem has arisen that the processing speed that can be achieved within microcomputers cannot be achieved with combination devices such as in-circuit emulators. It is desired to realize a single-chip microcomputer that can write data.

An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a microcomputer in which programs can be written and read from the outside.

[Means to solve the problem]

The microcomputer of the present invention is a microcomputer in which a nonvolatile read-only memory and an arithmetic processing section are integrated on the same device, and the arithmetic processing section is accessible from the outside. a first selector provided in between for selecting whether the memory is to be accessed externally or to the internal arithmetic processing section; and an input/output bus for accessing the microcomputer from the outside. A second selector that selects whether to be connected to the arithmetic processing unit or the first selector, and a control signal input means for controlling the first selector and the second selector. There is.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a first embodiment of the present invention.

The microcomputer 1 in FIG. 1 includes an arithmetic processing unit (hereinafter referred to as CPU) 2, a memory (EEPROM) 11, and a selector (
A first selector) 16, a selector (second selector) 5 provided between the input/output bus and the CPU 2, and an input circuit for a mode signal 17 that controls the selectors 5 and 16 are integrated.

Next, the operation will be explained. First, an operation mode is designated by a mode signal 17 from the outside. When the normal mode is designated, the selector 5 selects a bus so that signals are exchanged with the external address/data bus 7 only for CP[J2. That is, the address/control signal bus 8 is connected to the CPU 2 through the address/control signal bus 4, and the data bus 6 is connected to the CPU 2 through the data bus 3.
connected to.

At the same time, the selector 16 connects the address/control signal bus 13 for the memory 11 to the address/control signal bus 15 from the CPU 2, and connects the data bus 12 to the data bus 14 from C, PO2. Thereby, the CPU 2 can access the memory 11, and data can also be exchanged between the outside and the CPO 2.

Next, the case where the memory 11 is accessed from outside the microcomputer will be explained. First, the operation mode is set to memory access mode by the mode signal 17. When this mode is designated, the selector 5 disconnects the external address/data bus 7 from the CPU 2 and selects the selector 16.
Connect to.

As a result, the address/control signal bus 8 is connected to the address/control signal bus 10, and the data bus 6 is connected to the data bus 9. At the same time, the selector 16 disconnects the CPU 2 from the memory 11 and connects the address/control signal bus 1.
0 to the address/control signal bus 13, and data bus 9 to the data bus 12. As a result, the memory 11 can be accessed from outside the microcomputer 1 according to predetermined control.

FIG. 2 is a block diagram of a second embodiment of the invention. The difference from the first embodiment is that in the first embodiment, the mode signal 17 is given from the outside and one operation mode is determined accordingly, but in the second embodiment, access is always possible from either side. This is what is happening.

For this purpose, an access adjustment section 22 is provided.

When access is being made from one side, the access adjustment unit 22 issues a busy signal to the other side to avoid duplication. To access the memory 11, an access request is sent to the access adjustment unit 2 when a busy signal is not output.
This becomes possible by issuing the document in 2. A busy signal 20 and an access request signal 21 correspond to access requests from the outside, and a busy signal 19 and an access request signal 18 correspond to requests from the CPU 2. Based on these access request signals, the access adjustment unit 22 sends a mode signal 23 to the selector 5 and a mode signal 24 to the selector 16 to control the connection, and issues a G signal to the side that is not accessing.

The subsequent operations are the same as in the first embodiment.

〔Effect of the invention〕

As explained above, the present invention has a selector inside the microcomputer and can write and read programs from the outside into the built-in non-volatile read-only memory. It has the effect of allowing you to refer to and change the contents.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a first embodiment of the present invention, and FIG. 2 is a block diagram of a second embodiment.

1.1a...Microcomputer, 2...
... Arithmetic processing unit (CPU), 3, 6, 9, 12.14
・・・・・・Data bus, 4, 8, 10.13.15・
... Address/control signal bus, 5, 16...
...Selector, 7...External address/data bus, 11...Memory, 17, 23.24...-
...Mode signal, 18.21...Access request signal, 19.20...Busy signal, 22.
...Access Coordination Department.

Claims (1)

[Claims] In a microcomputer in which a nonvolatile read-only memory and an arithmetic processing section are integrated on the same device, and the arithmetic processing section is accessible from the outside, a microcomputer is provided between the memory and the arithmetic processing section, a first selector for selecting whether to access the external or internal arithmetic processing unit; and a first selector for selecting whether to access the microcomputer from the outside or to connect the input/output bus to the arithmetic processing unit. A microcomputer comprising: a second selector for selecting whether to be connected to the first selector; and a control signal input means for controlling the first selector and the second selector.