MICROCOMPUTER WITH BUILT-IN FLASH MEMORY

PROBLEM TO BE SOLVED: To measure a power voltage for flash memory control by using an ordinary tester, etc., by providing a CPU, etc., which turns a 1st voltage transmitting means OFF and a 2nd voltage transmitting means ON in voltage measurement mode and controls a read of the conversion result of an A/D converter. SOLUTION: The CPU 2 writes a code (for measuring, e.g. power source VAMP) in a 'measurement power source selection bit' of a flash control register 21. A code which turns OFF (closes) all transmission gates 50 to 52 as 2nd voltage means before the code is written is automatically set. The transmission gate 50 is turned ON (opened) and the voltage level (4.0 V) of the power source VAMP is transmitted to an input terminal 7n of a transmission gate 8n as a 1st voltage transmitting means in front of the A/D converter 5 through a wire. Then the CPU 2 actuates the A/D converter 5 to measure an analog potential from the input terminal 7n.