One chip microcomputer having programmable I/O terminals programmed according to data stored in nonvolatile memory

DETAILED DESCRIPTION A one-chip microcomputer according to the present invention is characterized by an initial reset circuit for producing a first initial reset signal having a first reset period and a second initial reset signal having a second reset period which is longer than the first reset period, an access circuit for gaining access to an address in a nonvolatile memory such as a built-in ROM to read data therefrom, and I/O buffer circuits.
A storage circuit and an I/O buffer connected to the selective function I/O terminal are provided in the I/O buffer circuit and a function of the selective function I/O terminal is selected in conformity with the data set in the storage circuit.
The data stored at a predetermined address in the nonvolatile memory is transferred to the storage circuit by operating the access circuit until the termination of the reset period of the second initial reset signal after the termination of the reset period of the first initial reset signal.
In this way, the desired function of the selective function I/O terminal can be selected by gaining access to an address in the nonvolatile memory and transferring the data thus stored therein to the storage circuit during the period between the end of the first reset and the second and of the reset signal.
In this case, the contents of write data can be altered by writing the data to the nonvolatile memory from the outside.
The optional function of the selective function I/O terminal thus becomes determined in accordance with the alteration.
An object of the present invention is therefore to provide a one-chip microcomputer equipped with a selective function I/O terminal with one of plural functions imparted to the I/O terminal to be selectable to another function.
Another object of the present invention is to provide a one-chip microcomputer equipped with ROM and an I/O terminal with so-called option and designed for writing to the ROM one of the functions imparted to the I/O terminal.
Still another object of the present invention is to provide a one-chip microcomputer equipped with a selective function I/O terminal which renders possible an efficient one-chip microcomputer system development