Sanyo Electric Co., Ltd.

Toru Watanabe

Susumu Yamada

Masanori Okubayashi

Shinichi Yamasaki

Susumu Kubota

Nobuhiro Arai

Noriyuki Ogata

Toshikazu Abe

A program for rewriting data in an address region B is written in an address region A which can be rewritten by an external PROM writer. After resetting the microcomputer and rewriting the program in address region A, the reset state is cancelled and the last address in address region A of the EEPROM (1) is then stored in a register (17). An address detector (18) prohibits rewriting in address region A based on an address value stored in the register (17).

Rewriting protection of a size varying first region of a reprogrammable

An EEPROM (1) is set to write mode when a program command to commence rewriting of data in region B in the EEPROM (1) is read out from region A. A CPU (2) then writes data specified by a latch (6) at an address in region B specified by a latch (4). In compliance with an inhibit signal INH, the CPU (2) now disregards the effects of the undefined output from the EEPROM (1) terminal DOUT.

Microcomputer using a non-volatile memory

When data are to be written in an EEPROM (1), a CPU (2) sets a flag (12). A voltage booster (13) boosts the power voltage in compliance with the setting of the flag (12). A voltage boost detector (14) detects whether the output of the voltage booster (13) is in voltage boost state. If the output of the voltage booster (13) is not in voltage boost state, a latch (15) is reset and the EEPROM (1) is not permitted to switch to write mode. As a result, it is possible to prevent incorrect data writing in the EEPROM (1) even when the flag (12) has been incorrectly set.

Microcomputer capable of preventing writing errors in a non-volatile

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Moriguchi, Japan

Toru Watanabe