Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
2002-02-25
2004-12-14
Verbrugge, Kevin (Department: 2188)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
C713S002000, C710S014000
Reexamination Certificate
active
06832285
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a microcomputer having a CPU (central processing unit) and a nonvolatile memory capable of being electrically written and erased, and relates in particular to a technology effective on one-chip microcomputers having flash memories for permitting or prohibiting programming and erasure on nonvolatile memories.
Electrically erasable and programmable nonvolatile memories such as flash memories, store information according to differences in threshold voltages programmed into the memory cells. This differential in threshold voltages in the flash memory is implemented by differences in the amount of electrons and positive holes stored by the floating gates. For example, applying a voltage at a high level relative to a threshold voltage in a stable thermal state is called the program status; and applying a voltage at a low level relative to the threshold voltage is called the erase status (The reverse of this definition may also be true.) There are no particular restrictions at this time but the erase operation to set the memory cell to erase status and the programming operation to set the memory cell to program status involve repeatedly applying a high voltage pulse and verifying the resulting threshold voltage. The writer mode and the boot mode are operating modes to allow programming and erasing the on-chip flash memory of the microcomputer. The writer mode is an operating mode treating the microcomputer as equivalent to a flash memory chip to program and erase the memory by connecting to a programming device such as an EEPROM writer. The boot mode is an operating mode for example, to establish communications to allow programming or erase with the microcomputer installed the system, by way of synchronized start-stop or a nonsynchronized serial interface (UART). The writer mode can be utilized to program data or program in an initialized state on the on-chip memory, prior to installation in the system. The boot mode on the other hand, can be utilized to reprogram information stored in the on-chip flash memory for program version upgrades or tuning data, prior to installation in the system.
The boot mode of the related art utilizes a serial interface as the basic interfacing method so a serial interface circuit such as for start-stop synchronizing, was incorporated into the system board of the microcomputer, when doing on-board programming by using the boot mode.
SUMMARY OF THE INVENTION
However, some systems essentially do not use start-stop synchronization. In disk drive systems such as CD-ROM (Compact Disk Read Only Memory), CD-RW (Compact Disk Rewritable), DVD-ROM (Digital Video Disk Read Only Memory), DVD-RAM (Digital Video Disk Random Access Memory) an interface such as an ATAPI (AT Attachment Packet Interface) or SCSI (Small Computer System Interface) is required. An area network interface called HCAN is used in automobile control systems such as for engines and transmissions. Even if the user's system board had interfaces such as ATAPI, SCSI or HCAN, if a serial interface for start-stop synchronizing was also required for on-board programming in boot mode, this created the problem of overhead costs in the user's system board.
This problem could be avoided by on-board programming in a memory storage area (in other words, user memory area) on an area of the flash memory where programming is freely allowed, in a user program mode capable of running programs. In other words, programming in advance, in writer mode, a dedicated user board communications protocol program such as for ATAPI in the user memory area. After programming this program, the microcomputer is mounted in the user's system board, and if that dedicated user board communications protocol program is then run by the CPU, the user memory area can be programmed with program version upgrades and data tuning performed.
However, when the dedicated user board communications protocol program was also written on the user area along with the user control program and tuning data, the user had to make it difficult to accidentally erase this dedicated user board communications protocol program, placing the large burden on the user of having to write a program. Further, when the CPU ran out of control in user program mode after installing the microcomputer in the system, and the processing program for running the communications protocol in user program mode was accidentally erased, there was no longer any chance of establishing an interface with the user system board for programming and erasing. Unless the microcomputer chip was removed, and the writer mode used, this method had the problem as clearly stated by the inventor himself, that programming could not be performed. In the specifications of the present invention, the term user broadly signifies the user of the semiconductor device such as the microcomputer. Therefore, if the manufacturer of the semiconductor device utilizes that semiconductor device in some manner, then that manufacturer is by definition a user.
The present invention therefore has the object of providing a microcomputer not prone to lose program information from the nonvolatile memory such as having communication protocols with the mounted board in the event the system is subjected to fatal errors such as deletion.
Another object of the present invention is to provide a microcomputer capable of ensuring an interface can be established with the microcomputer board separately supporting the communication protocol.
Yet, another object is to provide a microcomputer capable of preventing loss of stored information from the on-chip nonvolatile memory even if the CPU is running out of control.
The above described and other objects and unique features will become clear from the description of the present invention with reference to the accompanying drawings.
[1] An overview of a typical aspect of the invention as disclosed in these specifications is disclosed briefly as follows.
Besides a third area (user mat) for programming items such as a user (microcomputer user) control program, a second area (user boot mat) is provided in the on-chip nonvolatile memory of the microcomputer. This user boot mat is used as a memory storage area for programming for example, dedicated user communication protocols, and this mode also provides a user boot mode as a dedicated mode for running the program. This user boot mode is not capable of programming and erasing the user boot mat.
The effects rendered are as follows. (1) The microcomputer can make use of its own optional interface since a user boot mat capable of storing a dedicated user communication protocol is provided. (2) A serial interface need not always be provided on the user mounted board since an interface selected by the user can utilized to program and erase the nonvolatile memory. (3) A user optional program interface for programming and erasing can be implemented by separating the user boot mat and the user mat so that a control program for storage and use in the user mat can easily be made, even without programming a dedicated communication protocol program in the user mat. In other words, special measures for preventing erasure of the communications control program used in the user program mode are not needed. (4) The user boot mode started up from the user boot mat, is unable to program on or erase the user boot mat, so that information stored in the boot mat is not destroyed even when the system is running out of control, and even if the CPU runs out of control during debugging, damage will not extend to the program controlling the external interface so that the user mat can be freely programmed on-board the chip, without having to remove the microcomputer chip.
[2] A microcomputer of a detailed first aspect of the present invention includes a CPU, a nonvolatile memory having an electrically erasable and writable first area (boot mat), a second area (user boot mat) and a third area (user mat), and an operating mode specifier means. The operating mode specifier mea
Ishikawa Eiichi
Yada Naoki
Ho Thang
Miles & Stockbridge P.C.
Renesas Technology Corp.
Verbrugge Kevin
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