JPH07200523A - Microcomputer - Google Patents

Abstract

PURPOSE:To lay out a memory space of an external device (extention memory) which is added to a chip while securing a least necessary memory space for a storage such as a built-in ROM, etc., when a memory map is laid out for a single-chip microcomputer. CONSTITUTION:In reference to a single-chip microcomputer, a memory space used for a built-in ROM is divided into a working memory space and a non- working memory space based on the variable address value set on an area register. Then the non-working memory space is laid out in a memory space set for an extension memory. Thus it is possible to set/change the memory space of the built-in ROM to a least necessary space in response to the acutaul working state just by making a user set/change the variable address value even if the memory space of the built-in ROM is decided according to the storage capacity of the ROM when the microcomputer 18 shipped plant. Therefore the non-working memory space can be best used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology particularly effective when applied to a memory map design of a microcomputer, and further a single chip microcomputer. For example, allocation of a memory space of an external device added to the microcomputer. Related to useful technology.

[0002]

2. Description of the Related Art In a single chip microcomputer, the memory capacity of the read only memory (ROM), random access memory (RAM) and internal register on the chip is fixed, so that the memory map The design has also been completed by the manufacturer by the factory of the microcomputer. This memory map is divided into a memory space set based on the storage capacity of a ROM (built-in ROM) provided on the chip, a memory space based on the storage capacity of the built-in RAM, and further a memory space for built-in registers. . If the address of the memory map is 16
When given from "0000" to "FFFF" in the base system (64 kbytes), for example, the internal ROM memory space is 62 kbytes, the internal RAM memory space and the internal register memory space are 2 k The memory space is allocated in the manner of bytes. But,
In a system using a single-chip microcomputer in recent years, a user may connect an expansion memory (for example, an expansion RAM) to the outside in order to increase the memory capacity. However, if the memory map is determined by the manufacturer side before the microcomputer is shipped from the factory as described above, the memory space of the expansion memory connected to the microcomputer cannot be secured. Therefore, a method of substituting the memory space for the built-in ROM with the memory space for the extended memory is described in, for example, "H81534.53" issued by Hitachi Ltd. Semiconductor Division (1990).
6 Hardware Manual ", pages 67-72.

[0003]

However, the present inventors have clarified that the above-mentioned technique has the following problems. That is, in the method proposed above, the memory space for the built-in ROM is used as it is as the memory space for the expanded external device (extended memory), so that the memory space for the built-in ROM is limited. Defect occurs.

The present invention has been made in view of the above circumstances, and relates to a single chip microcomputer in which a memory map is allocated based on the storage capacity of a storage device such as a built-in ROM or RAM. ,
It is a main object of the present invention to provide a microcomputer capable of allocating a memory space of an external device added to the chip while securing the memory space of the built-in storage device. The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0005]

The typical ones of the inventions disclosed in the present application will be outlined below. That is, in the single-chip microcomputer of the present invention, when setting the memory space of the added external device, the memory space already set according to the storage capacity of the built-in read-only memory is actually A memory space where data is stored in
A register (area register) for setting an address indicating the boundary line is provided separately from the unused memory space, this address value is set in the area register, and unused based on this set address value. The memory space is distinguished and the unused memory space is allocated to the memory space for the external device.

[0006]

[Function] The memory space determined according to the storage capacity of the read-only memory built in the microcomputer can be changed to the memory space actually used only by setting / changing the value of the area register. , Unused memory space, and the unused memory space can be used as a memory space of an external device added to the microcomputer.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a memory map showing how to allocate a memory space of a single chip microcomputer, and FIG. 2 is a block diagram showing a procedure of determining a memory space by a central processing unit (CPU). As shown in FIG. 1, in the single chip microcomputer of this embodiment, a memory space of 64 kbytes (from "0000" to "FFFF" in hexadecimal notation) is reserved for the memory map. This memory space is a read only memory (RO) built in the microcomputer.
Based on the storage capacity of M), the storage capacity of the built-in random access memory (RAM), and the storage capacity of the built-in register, two reference address values (first and second reference address values). ) Is divided into three. (For example, the memory space for built-in ROM is 62 kbytes, built-in R
The memory space for the AM and the internal register is divided into a total of 2 kbytes. )

The memory space for the built-in ROM further includes
Variable address value described later (area register address value)
Are divided into a used memory space where the data stored in the built-in ROM is actually allocated and an unused memory space. Then, the unused memory space is used as an external I / O expansion area and is allocated to a memory space for an external device (for example, additional RAM) externally attached to the microcomputer.

The reason why the internal ROM memory space is divided into the used memory space and the unused memory space and the unused space is used as the external I / O expansion area as described above is as follows. That is, in a single-chip microcomputer, the storage capacity of the built-in ROM is
It is rare that the user actually uses the memory to the maximum extent, so that an unused space occurs in the memory space for the internal ROM. (If the user uses part of the storage capacity of the built-in ROM (for example, 48 Kbytes), the remaining part (14 Kbytes) of memory space is unused.) In a microcomputer system, an expansion memory such as an expansion RAM is often connected to a microcomputer as an external device, and there is a demand for providing a memory space for the expansion memory on the same memory map. Therefore, in the microcomputer system of the present embodiment, the built-in R that has already been set by the manufacturer based on the actually used capacity out of the storage capacity of the built-in ROM.
Variable address (boundary line address) for OM memory space
Is set, the memory space is further divided into a used memory space and an unused memory space, and the unused memory space is used as a memory space for an expansion memory (external expansion I / O area).

In the microcomputer in which the memory map is set in this way, the CPU compares the address value of the address signal with the first and second reference address values, respectively. When the address value is between the first and second reference address values, the built-in RAM is accessed, and when the address value is smaller than the second reference address value, the built-in register is accessed. When the address value is smaller than the first reference address value, the CPU further compares the address value with the variable address value according to the following procedure, and
The access is performed to either M or the extended memory (external device).

FIG. 2 shows that when the address value is smaller than the first reference address value, the control unit (control circuit) 10 of the CPU
4 is a control block diagram showing the procedure of an access process performed in FIG. As shown in this figure, in the control circuit 10 of the CPU, the address comparator 11 compares the address value of the address signal generated this time with the variable address value stored in the area register. The stored value of the area register can be set to a desired value by the user by operating an external switch provided in the microcomputer main body or a keyboard connected to the main body. Therefore, by this operation, the stored value is changed to the built-in RO.
The unused memory space can be used to the maximum extent if the required minimum value is set according to the data actually stored in M. When the address value this time is smaller than the variable address value by comparing the address values, a low level “0” control signal is output to the access signal comparator 12 to indicate access to the built-in ROM. On the other hand, when the address value this time is larger than the variable address value, the expansion RAM connected to the chip
A high-level “1” control signal is output to the access signal comparator 12 to indicate access to the (external device).

The access signal comparator 12 to which the control signal is input is further provided with a memory access signal generated when the internal ROM is accessed and an I / O access generated when the external device is accessed. Signals are input, and a final area discrimination signal is output based on these signals. Then, when the control signal is "0" and the memory access signal is input, a low level area determination signal "0" for instructing access to the internal ROM is output. On the other hand, when the control signal is "1" and the I / O access signal is input, the high-level area determination signal "1" for instructing access to the external device (extended memory) is output. The area discrimination signal thus obtained is used, for example, when the CPU executes a program stored in the built-in ROM, and is stored in the built-in ROM on condition that the area discrimination signal is "0". The stored program is executed. When the area discrimination signal is "1", the extended memory is accessed without executing the above program.

The variable address value is read by the CPU every time the microcomputer system rises. Therefore, when the stored contents such as the program of the built-in ROM is changed, if the variable address value is changed in advance by the operation of the external switch, the keyboard, etc., each time the system is started up. The memory space on the memory map can be changed.

As described above, in the single chip microcomputer of the present embodiment, the memory space for the built-in ROM is not used as the space actually used based on the address value set in the area register. This unused memory space is allocated to the memory space for the external device that has been added, so that the unused memory space is allocated according to the storage capacity of the internal ROM when the microcomputer is shipped from the factory. Built-in RO in memory map
Even if the M memory space is determined, the user can then change the built-in ROM memory space to the minimum necessary space according to the state of use. Then, the unused memory space remaining at this time can be used as the memory space of the external device.

Although the invention made by the present inventor has been specifically described based on the embodiments, the invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say. For example, in the above embodiment, an example in which the expansion RAM is expanded as the external device has been described, but the invention is not limited to this, and the setting of the memory map according to the present invention can be applied when another external storage device is expanded. In the above description, the invention mainly made by the present inventor has been applied to the setting of the memory map of the single-chip microcomputer system, which is the field of use which is the background of the invention, but the present invention is not limited thereto. However, it can be generally used for the technique of dividing the memory space of the memory map.

[0016]

The effects obtained by the representative one of the inventions disclosed in the present application will be briefly described as follows. That is, in the microcomputer of the present invention, while keeping the memory space of the built-in ROM to a necessary minimum, the unused area of the remaining memory space is
It can be used as a memory space of an expanded external device, and user convenience is improved.

[Brief description of drawings]

FIG. 1 is a memory map showing how to allocate a memory space of a single-chip microcomputer of this embodiment.

FIG. 2 is a block diagram showing a procedure of determining a memory space by a central processing unit (CPU).

[Explanation of symbols]

 10 Central Processing Unit Control Circuit 11 Address Comparator 12 Access Signal Comparator

Claims (3)

[Claims] 1. A read-only memory having at least a read-only memory and a central processing unit according to a storage capacity of the read-only memory.
A microcomputer in which a memory space for a memory is set is provided with an area register capable of setting / changing an address value, and the central processing unit is based on a predetermined address value set in the area register. And a control circuit for dividing an unused memory space from the read-only memory memory space and allocating the unused memory space to a memory space for an external device externally attached to the chip. Microcomputer characterized by. 2. The control circuit compares an address value indicated by an address signal with the predetermined address value, and based on a result of the comparison, whichever of the read-only memory and the external device is used. The microcomputer according to claim 1, wherein the microcomputer determines whether to access the address signal. 3. The control circuit recognizes a predetermined address value stored in the area register when the microcomputer is started up, and sets / changes a memory space based on the predetermined address value. The microcomputer according to claim 1 or 2, which is characterized.