Memory device system

A memory device system comprising:

• a first memory that has m lines (m is an integer not smaller than 2) of addresses and in which different pieces of data are respectively stored at the m lines of addresses, and a parity bit detecting an error of data is stored;
• a second memory that has m lines (m is an integer not smaller than 2) of addresses and in which same pieces of data as the pieces of data stored in the first memory are stored in an initial state;
• a first register that is connected with the first memory and stores only one piece of data divided into m pieces and stored in the first memory, in an order of the addresses in the first memory;
• a second register that is connected with the second memory and stores one piece of data divided into m pieces and stored in the second memory, the one piece of data having an address same as the address of the data of the first memory stored in the first register;
• a comparator that compares the piece of data stored in the first memory with the piece of data stored in the second memory;
• a transfer register that stores the piece of data of the first memory compared by the comparator;
• an error data register that stores the piece of data of the second register when the comparator determines that there is no matching between the piece of data of the first register and the piece of data of the second register;
• an error address register that stores an address of the second memory for the piece of data stored in the second register when the comparator determines that there is no matching between the piece of data of the first register and the piece of data of the second register;
• a parity calculation portion that calculates parity of all pieces of data stored in the transfer register and determines whether there is matching between the parity and the parity bit;
• and
• a controller that performs a predetermined control based on a calculation result by the parity calculation portion,
• wherein:
• after all pieces of data stored in the first memory are stored into the transfer register, the controller causes the parity calculation portion to determine whether there is matching between the parity of all pieces of data stored in the transfer register and the parity bit;
• when the parity calculation portion determines that there is parity matching,
• the controller causes the transfer register to transmit all pieces of data stored in the transfer register to an external circuit;
• when the parity calculation portion determines that there is no parity matching,
• the controller replaces the piece of data at the address stored in the error address register, out of the pieces of data stored in the transfer register, with the piece of data stored in the error data register, and then causes the parity calculation portion to again determine whether there is matching between the parity of all pieces of data stored in the transfer register and the parity bit, and when the parity calculation portion determines that there is parity matching, the parity calculation portion causes the transfer register to transmit all pieces of data stored in the transfer register to the external circuit.