JPH01184532A - Single chip microcomputer - Google Patents

Abstract

PURPOSE:To efficiently use a single chip microcomputer in which universal software is stored by changing a memory address position where the program start address information of the single chip microcomputer is stored. CONSTITUTION:When a mode signal MD is set at '0', two bits counting from the most significant order of a PC (program counter) 10 are set and remaining bits are reset by a reset signal, then, an address goes to 4000H. When the reset signal RESET is canceled, a microprogram is operated, and the contents of addresses 4000H and 4001H are fetched as the content of the PC 10 finally, then the execution of the program is started. Since the addresses 4000H and 4001H exist in an external memory area, the program can be executed from an appropriate address without performing a write processing on an internal ROM. Such state is valid for the pre-write of the universal program in the internal ROM in the single chip microcomputer and the usage of the microcomputer as a universal microcomputer.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention has a microcomputer, particularly a read-only memory (hereinafter referred to as ROM) and a central processing unit (hereinafter referred to as CPU) on the same semiconductor substrate. The present invention relates to a single-chip microcomputer in which various effective general-purpose programs are written and provided in a ROM in advance.

[Conventional technology]

An LSI in which a CPU, memory, and various I/O functions are mounted on the same semiconductor substrate is called a single-chip microcomputer, and it is literally possible to configure one electronic control system with one semiconductor chip.

Conventionally, the software (program) that operates this type of single-chip microcomputer is designed by an equipment designer, and this information is written to the ROM inside the microcomputer by requesting this information to the semiconductor manufacturer that manufactures the microcomputer and custom-made. The procedure to purchase it as a product was not completed. However, as the scale of the device becomes larger and its functions become more diverse, the amount and complexity of the microcombinator software 7 required for this device also increases. Naturally, the functions and performance of microcomputers themselves have improved dramatically, and the memory space that microcomputers can handle has also expanded. For this reason, programs are increasingly being placed in large-capacity external memory rather than in internal ROM.

Under such circumstances, it takes a great deal of effort and expense for software designers to design a huge amount of programs and correct their errors in a short period of time. Therefore, if programs useful for software design, such as a general-purpose operating system or function library, are written in the memory of a microcomputer in advance, the efficiency of software design can be greatly improved by using these programs.

However, in a conventional single-chip microcomputer with a built-in memory, the memory address for storing information for determining the start address of a program is located in the built-in ROM. - For example, single-chip microcomputer μP078C14 manufactured by NEC ■
The memory map is shown in FIG.

[Problems to be Solved by the Invention] In the conventional single-chip microcomputer described above, the memory address for storing information for determining the start address of a program is located in the internal ROM space. Even though programs useful for software design, such as the following, are written in advance in the internal ROM as general-purpose programs, it is always necessary to ask the semiconductor manufacturer to write specific information specifying the start address of each system. From the equipment system designer's perspective, it takes time to obtain a microcomputer, leading to delays in equipment manufacturing, and from the semiconductor manufacturer's perspective, the microcomputers for each system are custom-made, which increases costs. There are many shortcomings.

[Differences between the invention and the prior art]

The above-mentioned conventional program start address information is stored in the internal R
In contrast to a single-chip microcomputer that is fixedly held in the OM space, the present invention provides a single-chip microcomputer that stores general-purpose software by changing the memory address location for storing flocram start address information depending on the usage status of the single-chip microcomputer. The difference is that a chip microcomputer can be used efficiently.

[Means for solving problems]

The single-chip microcomputer of the present invention is a ROM
, a CPU and a peripheral I/O unit are configured on the same semiconductor substrate, and information for determining the start address of program execution is obtained from within the ROM based on a specific state setting signal applied from outside the single-chip microcomputer; It has means for selecting whether to obtain data from other storage means.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of a program address setting portion of a single-chip microcomputer that is an embodiment of the present invention. In Figure 1, 1o is the boogram counter (PC
) and has a length of 16 bits. 11 is an incrementer that increments the contents of the program counter; 12 and 13 are temporary registers TA;
It is TB.

14 represents an internal data bus. 21 is an inverter, and 22 and 23 are AND gates. Also, the output of the program counter (PC) /O is the internal address bus 15.
It has been derived.

Here, the operation of setting the program start address will be explained with reference to the flowchart of the microprogram for generating the reset address shown in FIG. 2 and the memory map shown in FIG. 3.

First, the PCIO is reset by the reset signal (RESET), but if the mode setting signal (MD) is logic level "1", all bits of the PCIO are reset and the contents become 0000H. The program starts running. oo by control of microprogram.

The contents of address H are TA12, and the contents of address OOIH are TE.
01 and finally transferred to PCIO, where the program starts running. Currently, 16 bytes are set in the internal ROM from addresses 0OOH to 3FF'F'H, so the program start address information is stored in the internal ROM.
However, in this state, the software of the microcomputer application device is relatively small, especially when all programs are written in the internal RO of 16 bytes.
It is valid if it falls within M.

Next, when the mode signal (MD) has a logical value of "0", the reset signal (RESET) sets the second bit from the top of PCIO and resets the remaining bits.
The content of O is 4000H. When the reset signal is released, the microprogram operates in the same way, and finally the contents of addresses 4000H and 4001H are taken in as the contents of PCIO, and program execution starts. 400
Since 0H and 4001H are located in the external memory area, the software designer can start program execution from an appropriate address without any special writing process to the internal ROM. This condition is a single hit.

This is effective when a general-purpose program is written in the internal ROM of a microcomputer in advance and the program is treated as a general-purpose microcomputer.

[Embodiment 2] Further, another embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a block diagram of the program address setting part of a single-chip microcomputer according to another embodiment of the present invention, FIG. 5 is a flowchart of a microprogram for generating a reset address, and FIG. 6 is a block diagram of the program address setting part of a single-chip microcomputer of this embodiment. This is the memory map of FIG. 4 is basically the same as FIG. 1, and the same blocks are given the same numbers. The difference is that PCIO uses a reset signal (RES
ET), and 16 constant generators (CONST) are added.

In this embodiment, the microprogram determines which program start address is to be set.

That is, according to the microprogram shown in FIG. 5, if the mode setting signal MD is "1", the program start address information is 0000H.

Address 0001H is assigned. If MD is "θ", the constant generator 16 writes 40H and OOH to TA and TB, respectively, and transfers them to PCIO to generate program start address 4000H.

[Effects of the Invention] As explained above, the present invention provides a means for obtaining program start address information from both the internal ROM and other sources using the state setting signal.
A microcomputer with a general-purpose program written in the OM in advance can be treated as a general-purpose product, which has a great effect on shortening the software development period and reducing the cost of the microcomputer itself.

[Brief explanation of the drawing]

FIG. 1 shows a single hitch according to a first embodiment of the present invention. FIG. 2 is a block diagram of a program address setting part in a microcomputer, FIG. 2 is a flowchart of a microprogram for generating a program start address, and FIG. 3 is a memory map. FIG. 4 is a block diagram of a program address setting part in a single-chip microcomputer according to another embodiment of the present invention, FIG. 5 is a flowchart of a microprogram for generating a program start address, and FIG. 6 is a memory map. FIG. 7 is a memory map of a conventional single-chip microcomputer. In Figures 1 and 4, /O...Program counter (PC), 11.
...Incrementer (INC), 12, 13...
... Temporary register, 14 ... Internal data bus, 15 ... Internal 7 address bus, 16.
...Constant generator (CONST), 21...
・Inverter, 22, 23...and gate. Agent Patent Attorney Uchihara Oto, 251st 3rd Diagram 4 Okina I5 Figure ￥J1

Claims (1)

[Claims] Read-only memory (ROM) and central processing unit (CPU)
) and a peripheral I/O unit are configured on the same semiconductor substrate. A single-chip microcomputer characterized by having means for selecting whether to obtain information from within the ROM or from other storage means.