JPS6243229B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a one-chip microcomputer in which the contents of a memory can be easily checked from the outside.

As is well known, an electronic computer consists of a central processing unit (CPU), memory that stores instructions and processing data,
The basic components are input/output devices (I/O). The so-called microcomputers that started with processors such as Intel's 4004 in the early 1970s are no exception, but there are very few devices that are called microcomputers, and they are mainly silicon-based.
Its distinctive feature is that it is constructed using MOS LSI. With the increase in the integration of LSIs, when microcomputers first appeared, a device that implemented the functions of a CPU on a single semiconductor chip was called a microprocessor or microcomputer, but today it has become possible to use memory such as RAM or ROM. Furthermore, the I/O control section is now being implemented on the same chip. Due to the integration of such functions, a simple information processing system can be configured with one or a few LSIs and a few external components, resulting in a significant increase in cost and performance. Various problems have arisen in terms of use.

One problem is data transfer. As mentioned above, due to the improvement in IC integration, the CPU part and the RAM part that stores processing data, etc. are often mounted on the same chip, and as the storage capacity of the RAM increases, A request arises to input and output data to RAM. For example, data exchange between the RAM and external I/O, the RAM
Examples include monitoring the operation of a microcomputer by checking a certain part of it.

Extracting the contents of RAM to the outside or writing data to RAM from the outside can be performed with current devices without any modification if the CPU is used. However, this method places a heavy burden on the CPU, resulting in poor throughput. Also
Microcomputers with built-in RAM often have instruction sequences (programs) built into the ROM, making it difficult to control the operating state of the chip because it is difficult to tell from the outside. these are,
This can be improved by using a DMA method that exchanges data between memory and I/O without going through the CPU. However, the DMA method generally uses a parallel transfer method using a common bus, but if such a method is used in a microcomputer, a large number of terminal pins (eight for data transfer alone if data is sent in bytes) are required. This is a problem. Moreover, if the contents of the RAM are to be exported for debugging purposes, these DMA terminal pins will become unnecessary when development is completed and mass production begins.

The present invention has been made in view of the above points, and
We devised a method that allows the contents of RAM to be easily exported externally without placing any burden on the CPU and using a small number of terminal pins. That is, the present invention provides a one-chip microcomputer in which a central processing unit and a random access memory are mounted on a semiconductor chip. write the type of data,
The present invention is characterized in that when the central processing unit sends a signal to the control device, the control device sequentially and serially transmits the contents of the register to the outside.This will be explained below with reference to embodiments. do.

FIG. 1 shows a first embodiment of the invention. 10 is a semiconductor chip, which includes a CPU 12 and a RAM 1.
4. Various functional circuits 16, a serial I/I/
A microcomputer is configured by mounting the O18, its transmission register 20, and the like. In the present invention, in order to monitor the operation of the CPU from the RAM contents, a memory area 14a is defined in the RAM 14 in which data suitable for the monitoring is written, and a register 22 in which the same data as that of the memory area 14a is written and its control A circuit 24 is provided. In this example, the storage capacity of the memory area 14a is 1 byte, and the register 2
Similarly, 2 has a capacity of 1 byte. Although this amount of capacity is often sufficient for checking the functions of the CPU, it is of course possible to use a larger capacity such as 2 bytes, 3 bytes, etc.

In this device, the CPU performs arithmetic operations, and the preselected types of the processing results are stored in the RAM 1.
When writing to the area 14a of No. 4, the data is also written to the register 22 via the control device 24. The same holds true when the next type of data is written to area 14a, and thus register 22 is constantly updated to hold the same contents as area 14a. When it is desired to send the above type of data to the outside, the CPU gives a signal instructing DMA (direct memory access) to the control device 24, and the control device transfers the contents of the register 22 to the transmission register 20, and also transfers the contents of the register 22 to the transmit register 20, and
The contents of the register 22 are sequentially read out using the same clock as used in O18 and serially transmitted to the outside. Of course, in this case, the above operation must not coincide with writing new data to the register 22 and sending data from the serial I/O to the outside, but the CPU controls such timing.

According to this method, the CPU sends DMA to the control device 24.
It is possible to send the stored contents of a specific RAM area to the outside by simply giving a command, and since operations such as sequentially reading RAM are not required, the CPU load does not increase and data can be sent quickly. Since serial transmission is used, only one terminal pin is required, and if a serial I/O is provided, the terminal pin for data transmission and reception can be used, which is convenient. When reading the contents of the RAM for the purpose of debugging a program, the register 22 and the control device become unnecessary once the development stage of the LSI is completed and mass production begins. Therefore, although these may be disabled, they may of course be allowed to remain, in which case they can be used to check the functionality of the LSI while it is in operation.

FIG. 2 shows a second embodiment of the invention. In FIG. 1, one or more specific bytes of data in the RAM 14 are taken out to the outside, but in FIG. 2, only the first bit of a data group of 8 or an integral multiple thereof is taken out to the outside. The storage capacity of the register 22 is therefore one or more bytes, and each time the CPU 12 writes a preselected type of data to the RAM 14, the first bit is stored in area 1.
4a and also writes to the register 22. As a result, the contents of the register 22 become the same as the contents of the first bit storage area 14a of the RAM 14, and are constantly updated. Reading is the same as in Figure 1, and the CPU
12 issues a DMA command to the control device 24. The first bit of data may indicate the type of data, and by monitoring these, it is possible to monitor the functions of the CPU, etc.

In order to send a large number of data groups in the RAM 14 to the outside, it is possible to read them from the RAM 14 while sending them out as shown in FIG. 3, which eliminates the need for a large capacity shift register 22.
An address counter 26 for reading out the area 14a of No. 4, and a control circuit 28 for avoiding conflict between accesses from the CPU 12 to the RAM 14 and accesses by the address counter 26 are required. Note that 30 is the same type of transmission register as 20, and is in area 1.
This is for data transmission of 4a.

As explained above, according to the present invention, specific data in the RAM of a one-chip microcomputer can be
It is extremely effective because it can be sent to the outside without bothering the CPU or requiring a large number of terminal pins.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams for explaining an embodiment of the present invention, and FIG. 3 is a diagram for explaining another possible example. In the drawing, 10 is a semiconductor chip, 12 is a central processing unit, 14 is a random access memory, 22 is a register, and 24 is its control unit.

Claims (1)

[Claims] 1. In a one-chip microcomputer in which a central processing unit and a random access memory are mounted on a semiconductor chip, the chip is provided with a register and its control device, and the register is also used to store a predetermined type of information that the central processing unit writes to the random access memory. A one-chip microcomputer characterized in that data is written and when the central processing unit sends a signal to the control device, the control device serially transmits the contents of the register to the outside.