Non-volatile semiconductor storage device and method of testing the same
Provided is a non-volatile semiconductor storage device which can be downsized with a simple circuit without impairing the function of an error correcting section, and a method of testing the non-volatile semiconductor storage device. An error correction circuit is configured to perform error detection and correction of merely the same number of bits as data bits, and a circuit for performing error detection and correction of check bits is omitted to downsize the circuit. A multiplexer for, in a testing state, replacing a part of the data bits read out from a storage element array with the check bits, and inputting the check bits to the error correction circuit is provided. Thus, error detection and correction of the check bits are performed to enable shipment inspection concerning the check bits as well.
1. A non-volatile semiconductor storage device, comprising:
a non-volatile semiconductor storage element array for storing data bits and check bits, the non-volatile semiconductor storage element array comprising one unit including an m-data-bit storage element and an n-check-bit storage element which forms a basic unit;
an error correction code generating circuit for generating an error correction code based on the data bits and the check bits of the one unit read out from the non-volatile semiconductor storage element array;
a control signal generating circuit for outputting a control signal for switching between a normal mode and a test mode;
a multiplexer for selecting between normal mode data and test mode data based on the control signal to output selected one of the normal mode data and the test mode data, wherein the test mode data comprises a total of m bits of data including n check bits, 2 fixed bits and a predetermined number of data bits corresponding to a number of m-(n+2); and
an error correction circuit for performing error correction on inputted m data bits based on the error correction code, wherein the error correction circuit corrects, in the test mode, the total of m bits of data including the n check bits.
2. A non-volatile semiconductor storage device according to claim 1 , wherein in the test mode, the error correction code corresponds to the test mode data.
3. A non-volatile semiconductor storage device according to claim 1 , further comprising a control gate (CG) bias switching circuit,
wherein the control gate (CG) bias switching circuit applies, to the non-volatile semiconductor storage element array, a normal bias voltage, or alternatively, an inspection bias voltage.
4. A method of testing a non-volatile semiconductor storage device, the method comprising:
writing, in a non-volatile semiconductor storage element array for storing m data bits and n check bits, one of 0 and 1 to all of the data bits and the check bits;
reading out the m data bits and the n check bits from the non-volatile semiconductor storage element array;
generating, by an error correction code generating circuit, an error correction code based on the m data bits and the n check bits;
switching, by a multiplexer, between normal mode data and test mode data, the test mode data having m bits of data including the n check bits,
outputting, by the multiplexer, corresponding one of the test mode data and the normal mode data; and
performing, by an error correction circuit, error correction using the test mode data which includes the n check bits, 2 fixed bits and a predetermined number of data bits corresponding to a number of m-(n+2).
5. A method of testing a non-volatile semiconductor storage device according to claim 4 , further comprising applying, by a control gate (CG) bias switching circuit, a normal bias voltage, or alternatively, an inspection bias voltage to the non-volatile semiconductor storage element array.