FAULT DETECTING METHOD FOR RAM

PURPOSE:To detect a fault of the RAM at a high-processing speed with a simple program. CONSTITUTION:Three registers are prepared in a CPU; and original data in a used area in the RAM are inputted in the 1st register and also saves in the 2nd register, and the bits of the original data in the 1st register are inverted. After the inverted data are written in the same address in the used area, the inverted data are inputted to the 1st register again and the inverted data in the 1st register and the original data saved in the 2nd register are added, bit by bit. Then the addition data are written in the 3rd register and it is decided whether the RAM is normal or abnormal according to whether or not the data in the 3rd register includes a bit '0'.