JP2002287994A - Microcontroller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microcontroller including a nonvolatile memory enabling to use the entire range of the nonvolatile memory as a range for a user program or data, without increasing the area of a chip. SOLUTION: A serial interface 16 and a DMA 17 transfer a program controlling rewriting of a flash memory 12 from an exterior device 30 to a RAM 14 in an early state. Under the condition that an on-board rewriting mode signal SM is inputted, a reset vector converting circuit 20 outputs an address of a RAM 13 storing a program instead of a reset vector when a CPU 22 outputs a storing address of the reset vector. Thereby, the CPU 13 executes a rewriting control program stored in the RAM 14 just after releasing a reset.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a technique relating to a microcontroller having a built-in nonvolatile memory.

[0002]

2. Description of the Related Art In recent years, a microcontroller having a built-in nonvolatile memory such as an electrically erasable and writable flash memory has been programmed with respect to the nonvolatile memory when the microcontroller is mounted on a system, that is, on-board. Various methods have been proposed for rewriting and changing storage contents such as data.

[0005] The rewriting mode of the nonvolatile memory includes C
There are two different modes, an on-board rewrite mode in which rewriting is performed under the control of the PU, and a PROM rewrite mode in which rewriting is performed under the control of an external device such as a general-purpose PROM writer. The PROM rewrite mode is mainly applied to writing of initial data and an initial program before the microcontroller is mounted on the system. On the other hand, the on-board rewrite mode is properly used for changing a program immediately before shipment of a product in which a microcontroller is mounted, upgrading a program version after shipment, and the like.

More specifically, in the PROM rewrite mode, the nonvolatile memory is in a state where it can be directly accessed from the outside by an external device such as a general-purpose PROM writer.
Etc. are in a state separated from the nonvolatile memory.

On the other hand, in the case of the on-board rewrite mode, a rewrite mode determination program for determining whether or not the rewrite mode is the on-board rewrite mode is provided in a predetermined area of the non-volatile memory. And a transfer control program for transferring the rewrite control program to be transferred to the RAM. If the CPU recognizes that the mode is the on-board rewrite mode by executing the mode determination program, the CPU executes the transfer control program to operate the serial interface and DMA which are peripheral functions generally mounted on the microcontroller. Then, the rewriting control program is transferred from the external device to the RAM. After the transfer,
The processing of the CPU shifts to the execution of a rewrite control program on the RAM, whereby erasing and writing to the nonvolatile memory are performed.

The above-described on-board rewriting method is a method in which a mode determination program and a transfer control program are previously written in a nonvolatile memory to be rewritten. Separately from this method, the transfer control program is stored in a mask ROM different from the nonvolatile memory to be rewritten, and in the on-board rewrite mode, the transfer control program in the mask ROM is executed. And transfer the rewrite control program to the RAM,
A method of rewriting the nonvolatile memory by transferring the processing of the CPU to a transfer program on the RAM has also been proposed.

FIG. 7 is a diagram showing a configuration of a microcontroller in which a mode determination program and a transfer control program are previously written in a nonvolatile memory. FIG. 8 shows a nonvolatile memory in which a transfer control program is stored in a mask ROM. FIG. 3 is a diagram illustrating a configuration of a microcontroller.

First, how the on-board rewriting is performed in the configuration shown in FIG. 7 will be described. External device 5
8 outputs a reset release signal and an on-board rewrite mode signal to the microcontroller 50. The CPU 51 that has released the reset executes the mode determination program stored in the flash memory 52 as the nonvolatile memory, recognizes the states of the data terminal and the clock terminal, and determines whether or not the mode is the on-board rewrite mode. When the onboard rewrite mode is recognized, the CPU
51 executes the transfer control program stored in the flash memory 52,
It controls the MA 57 to receive the rewrite control program from the external device 58 and transfers it to the RAM 53. When the transfer of the rewrite control program to the RAM 53 is completed, the CPU
51 shifts the execution of the instruction to a program on the RAM 53, executes the transferred rewrite control program, and erases / writes the flash memory 52 while receiving the user program and data to be written from the external device 58.
Execute writing.

Next, how the on-board rewriting is performed in the configuration of FIG. 8 will be described. External device 6
9 outputs a reset release signal and an on-board rewrite mode signal to the microcontroller 60. The CPU 61 that has released the reset recognizes the state of the data terminal and the clock terminal and determines whether or not the mode is the on-board rewrite mode by hardware. When recognizing the onboard rewrite mode, the CPU 61 sets the mask ROM 68
, And controls the serial interface 66 and the DMA 67 to receive the rewrite control program from the external device 69 and transfer it to the RAM 63. When the transfer of the rewrite control program to the RAM 63 is completed, the CPU 61 executes the instruction to the RAM 63.
The program shifts to the above program, executes the transferred rewrite control program, and executes erasing / writing to the flash memory 62 while receiving a user program or data to be written from the external device 69.

[0010]

However, in the conventional configuration as shown in FIG. 7, the CPU always starts the access from the address in the nonvolatile memory, so that the mode determination necessary for controlling the on-board rewriting is performed. It has become necessary to write a program or a transfer control program in the nonvolatile memory itself in advance. As a result, there is a problem that the entire area of the nonvolatile memory cannot be used as an area for the user program or data.

In a configuration as shown in FIG. 8, the transfer control program is stored in a mask ROM separate from the non-volatile memory so that the entire area of the non-volatile memory can be used as a user program or data area. Since a mask ROM has to be added as hardware, the chip area is increased, and the chip cost is increased.

In view of the above problems, it is an object of the present invention to provide a microcontroller with a built-in nonvolatile memory that makes it possible to utilize the entire area of the nonvolatile memory as a user program or data area without increasing the chip area. And

[0013]

Means for Solving the Problems To solve the above-mentioned problems, a solution taken by the present invention is to provide a CPU as a microcontroller, a nonvolatile memory whose storage contents can be electrically erased and written, and And a CPU configured to execute a program for controlling rewriting of the non-volatile memory stored in the RAM when reset is applied in an on-board rewriting mode and after reset is released. is there.

According to the present invention, the CPU can directly execute the rewrite control program stored in the RAM after the reset is released, so that the mode determination program and the transfer control program are previously stored in the nonvolatile memory. There is no need to write it. As a result, the entire area of the nonvolatile memory can be used as a user program and data area.

In the microcontroller according to the present invention, when the CPU outputs the storage address of the reset vector while the on-board rewrite mode signal is input, the microcontroller outputs the reset vector instead of the reset vector. And a reset vector conversion circuit for outputting an address of the RAM in which the program is stored.

In the microcontroller according to the present invention, when the CPU outputs a storage address of a reset vector in a state where an on-board rewrite mode signal is input, the storage address is stored in the microcontroller. RA for converting to the address of the RAM and outputting
Preferably, an M address output circuit is provided.

Further, the microcontroller according to the present invention comprises a serial interface for performing data communication with an external device, and the data received by the serial interface to the R interface without the operation of the CPU.
A DMA for transferring the program to the AM, wherein the serial interface and the DMA are capable of receiving the program from the external device upon receiving an on-board rewrite mode signal, and capable of transferring the received program to the RAM. It is preferable that

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a diagram showing a configuration of a microcontroller with a built-in nonvolatile memory according to a first embodiment of the present invention. In FIG. 1, 10 is a microcontroller with built-in nonvolatile memory, 11 is a CPU, 1
2 is a flash memory as an electrically erasable and writable nonvolatile memory to be rewritten, 13 is a RAM, 14 is an address bus, 15 is a data bus, 16
Reference numeral 17 denotes a serial interface that communicates with the external device 30; and 17, a DMA that transfers data received by the serial interface 16 to the RAM 13 in hardware without going through the operation of the CPU 11. External device 30
Supplies a rewrite control program for controlling rewriting of the flash memory 12, and other programs and data to the microcontroller 10.

The microcontroller 10 shown in FIG.
When a reset is applied in the on-board rewrite mode, the CPU 11 executes a program for controlling rewriting of the flash memory 12 stored in the RAM 13 after the reset is released. 20
Is a reset vector conversion circuit provided so that the CPU 11 can directly execute the program on the RAM 13 after releasing the reset. Reset vector conversion circuit 20
When the CPU 11 outputs the storage address of the reset vector in a state where the on-board rewrite mode signal SM is input, the CPU 1 outputs to the CPU 1 the RAM 1 storing the rewrite control program instead of the reset vector.
The address 3 is output.

FIG. 2 is a diagram showing an example of the configuration of the reset vector conversion circuit 20. In FIG. 2, reference numeral 21 denotes a CPU1.
The address comparator 22 determines whether or not the address output from 1 is a reset vector address. When the on-board rewrite mode signal SM is input and the output of the address comparator 21 is active, the address comparator 22 is set to “H”. An AND gate 23 for outputting a level, 23 is a RAM address generator for outputting an address value in the RAM 13 at which the rewrite control program is stored, and 24 is a RAM address generator 2 when the output of the AND gate 22 is at "H" level.
3 is a selector that outputs the value of the data bus 15 when the output is at the “L” level while the output of the data bus 15 is selected.

FIG. 3 shows an address space of the memory according to the present embodiment. As shown in FIG. 3, from the start address X'00000 '(X represents a hexadecimal number) of the RAM 13,
A rewrite control program is stored. Further, a reset vector is stored at the head address X'04000 'of the flash memory 12. That is, the address comparator 21 in FIG. 2 determines whether the address output from the CPU 11 is X'04000 ',
M address generator 23 outputs address X'00000 '.

The operation of the thus configured microcontroller according to the present embodiment will be described below.

First, the external device 30 outputs an on-board rewrite mode signal SM to the microcontroller 10, and subsequently outputs a rewrite control program for controlling rewriting of the flash memory 12. The serial interface 16 and the DMA 17 are a CPU
In an initial state in which the control from 11 is not performed, data input from the outside can be transferred to the RAM 13. That is, the rewrite control program is received from the external device 30 and transferred to the RAM 13.

As shown in FIG. 4, the serial interface 16 and the DMA 17 include control registers 31 and 32.
The reset values of the control registers 31 and 32 are changed according to the state of the on-board rewrite mode signal SM. For example, in the configuration of FIG. 4A, the reset state of the register output is “L” level, and when the on-board rewrite mode signal SM is “H”, the register output can be changed to “H”. . FIG. 4
In the configuration of (b), the reset state of the register output is “H” level, and the on-board rewrite mode signal S
When M is “H”, the register output can be changed to “L”.

When the transfer of the rewrite control program to the RAM 13 is completed, the external device 30 outputs to the microcontroller 10 a signal for releasing the reset.
The CPU 11 that has released the reset outputs the reset vector address mapped on the flash memory 12 to read the memory address value (reset vector address value) that jumps after the reset is released.

The reset vector address is the address bus 1
4, in the reset vector conversion circuit 20, the address comparator 21 outputs “H” level.
At this time, the on-board rewrite mode signal SM is also “H”.
Therefore, the AND gate 22 outputs an “H” level to the selector 24, and the selector 24
Output of RAM address generator 23, ie, address X
'00000' is output to the CPU 11.

As a result, the CPU 11 recognizes the start address X'00000 'of the RAM 13 as the contents of the reset vector address, and starts executing the rewrite control program on the RAM 13. Then, while receiving a program or data to be written from the external device 30, the flash memory 12 is erased and written.

(Second Embodiment) FIG. 5 is a diagram showing a configuration of a microcontroller with a built-in nonvolatile memory according to a second embodiment of the present invention. 5, the same reference numerals as in FIG. 1 denote the same components as in FIG.

The microcontroller 10A shown in FIG.
Similar to the first embodiment, when reset is applied in the on-board rewrite mode, the CPU 11 executes a program for controlling rewriting of the flash memory 12 stored in the RAM 13 after reset release. It is configured. Reference numeral 40 denotes a RAM address output circuit provided so that the CPU 11 can directly execute a program on the RAM 13 after releasing the reset. When the CPU 11 outputs the storage address of the reset vector while the on-board rewrite mode signal SM is input, the RAM address output circuit 40 changes the storage address to the RAM 1 in which the rewrite control program is stored.
3 and output.

FIG. 6 is a diagram showing an example of the configuration of the RAM address output circuit 40. In FIG. 6, reference numeral 41 denotes the CPU 1
The address comparator 42 determines whether or not the address output from 1 is a reset vector address. When the on-board rewrite mode signal SM is input and the output of the address comparator 41 is active, “H” is set. An AND gate 43 for outputting a level, an address converter 43 for converting a reset vector address into an address value in which a rewrite control program is stored in the RAM 13 when the address output from the CPU 11 is a reset vector address, and a reference numeral 44 for A
When the output of the ND gate 42 is at "H" level, the selector selects the output of the address converter 43, and when it is at "L" level, it is a selector that outputs the address value output from the CPU 11.

The operation of the microcontroller according to the present embodiment configured as described above will be described below.

First, the external device 30 sends an on-board rewrite mode signal SM to the microcontroller 10A.
Then, a rewrite control program for controlling rewriting of the flash memory 12 is output. The serial interface 16 and the DMA 17
In the initial state where the control from U11 is not performed,
Data input from the outside can be transferred to the RAM 13. That is, the rewrite control program is received from the external device 30 and transferred to the RAM 13.

When the transfer of the rewrite control program to the RAM 13 is completed, the external device 30 outputs a signal for releasing the reset to the microcontroller 10A. The CPU 11 that has released the reset outputs the reset vector address mapped on the flash memory 12 to read the memory address value (reset vector address value) that jumps after the reset is released.

When the reset vector address is output, in the RAM address output circuit 40, the address comparator 41 outputs "H" level. At this time, since the on-board rewrite mode signal SM is also at the “H” level, the AND gate 42 sets the “H” level to the selector 4.
4 is output. The selector 44 is an address converter 4
3, the address value translated by
'00000' is output to the address bus 14.

As a result, the CPU 11 recognizes the start address X'00000 'of the RAM 13 as the contents of the reset vector address, and starts executing the rewrite control program on the RAM 13. Then, while receiving a program or data to be written from the external device 30, the flash memory 12 is erased and written.

As described above, according to each of the above embodiments,
By setting the serial interface and the DMA to receive data output from the external device in the initial state, the rewrite control program can be transferred to the RAM. Also, the reset vector conversion circuit 2
0 and the RAM address conversion circuit 40
However, after the reset is released, the rewrite control program transferred to the RAM 13 can be directly executed. That is, the program can be started from the RAM after the reset is released, so that it is not necessary to previously write the mode determination program and the transfer control program on the flash memory 12. As a result, the entire area of the flash memory 12 can be used as a user program and data area. Further, since it is not necessary to store the transfer control program in a memory area different from the nonvolatile memory such as a mask ROM or the like, there is no increase in chip area.

[0038]

As described above, according to the present invention, the CPU
However, after the reset is released, the program stored in the RAM can be executed, so that the user can utilize the entire area of the nonvolatile memory as the area for the user program and data. In addition, since it can be realized by adding a small number of circuits, an effect of high cost performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a microcontroller with a built-in nonvolatile memory according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a reset vector conversion circuit according to the first embodiment of the present invention.

FIG. 3 is an address space of a memory according to the first and second embodiments of the present invention.

FIG. 4 is a diagram showing register control in a serial interface and DMA.

FIG. 5 is a diagram showing a configuration of a microcontroller with a built-in nonvolatile memory according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating a configuration of a RAM address output circuit according to a second embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of a conventional microcontroller with built-in nonvolatile memory.

FIG. 8 is a diagram showing a configuration of a conventional microcontroller with a built-in nonvolatile memory.

[Explanation of symbols]

 10, 10A Microcontroller 11 CPU 12 Flash memory (non-volatile memory) 13 RAM 16 Serial interface 17 DMA 20 Reset vector conversion circuit 30 External device 40 RAM address output circuit SM On-board rewrite mode signal

Claims (4)

[Claims] 1. A CPU comprising: a CPU; a non-volatile memory whose storage content is electrically erasable and writable; and a RAM. A microcontroller configured to execute a program for controlling rewriting of the nonvolatile memory stored in the microcontroller. 2. The microcontroller according to claim 1, wherein when the CPU outputs the storage address of the reset vector in a state where the on-board rewrite mode signal is input, the CPU outputs the reset vector instead of the reset vector. ,
A microcontroller, comprising: a reset vector conversion circuit that outputs an address of the RAM in which the program is stored. 3. The microcontroller according to claim 1, wherein when the CPU outputs a storage address of a reset vector in a state where an on-board rewrite mode signal is input, the storage address is stored in the program. A microcontroller comprising a RAM address output circuit for converting the data into an address of the RAM and outputting the converted address. 4. The microcontroller according to claim 1, wherein a serial interface that performs data communication with an external device, and a DMA that transfers data received by the serial interface to the RAM without going through the operation of the CPU. The serial interface and the DMA receive an on-board rewrite mode signal, receive the program from the external device, and transfer the received program to the RAM. A microcontroller, characterized in that: