Semiconductor memory device and system with redundant element
A semiconductor memory device includes a memory cell array, a redundant element, an address specifying circuit configured to select one of a plurality of addresses as a redundancy address in response to a switchover signal, a decoder circuit configured to select the redundant element in response to an externally applied address that matches the redundancy address selected by the address specifying circuit, and a test mode setting circuit configured to change the switchover signal in response to an externally applied input, thereby to cause the redundancy address assigned to the redundant element to be switched between different ones of the plurality of addresses.
1. A semiconductor memory device, comprising:
a memory cell array;
a redundant element;
an address specifying circuit configured to select one of a plurality of addresses as a redundancy address in response to a switchover signal;
a decoder circuit configured to select the redundant element in response to an externally applied address that matches the redundancy address selected by the address specifying circuit; and
a test mode setting circuit configured to change the switchover signal in response to an externally applied input, thereby to cause the redundancy address assigned to the redundant element to be switched between different ones of the plurality of addresses.
2. The semiconductor memory device as claimed in claim 1 , wherein the address specifying circuit includes:
a first address specifying circuit configured to specify a first address;
a second address specifying circuit configured to specify a second address; and
a select circuit configured to select one of an output of the first address specifying circuit and an output of the second address specifying circuit in response to the switchover signal.
3. The semiconductor memory device as claimed in claim 2 , wherein the first address specifying circuit produces as the output thereof a first bit pattern indicative of bitwise matches or mismatches between the first address and an externally applied address, and the second address specifying circuit produces as the output thereof a second bit pattern indicative of bitwise matches or mismatches between the second address and the externally applied address.
4. The semiconductor memory device as claimed in claim 3 , further comprising a memory circuit configured to store a defective address in a nonvolatile manner, and wherein the first address specifying circuit is configured to selectively invert bits of the first bit pattern in response to respective bit values of an output of the memory circuit.
5. The semiconductor memory device as claimed in claim 1 , wherein the address specifying circuit includes:
an address specify circuit configured to specify a first address;
a register configured to store an address bit pattern that is externally applied; and
a select circuit configured to select one of the first address and a second address responsive to the address bit pattern stored in the register in response to the switchover signal.
6. The semiconductor memory device as claimed in claim 5 , wherein the address specify circuit is configured to produce a bit pattern indicative of bitwise matches or mismatches between the first address and an externally applied address in response to selection of the first address by the select circuit, and to produce a bit pattern obtained by selectively inverting respective bits of the bit pattern indicative of bitwise matches or mismatches depending on respective bit values of the address bit pattern in response to selection of the second address by the select circuit.
7. The semiconductor memory device as claimed in claim 6 , further comprising a memory circuit configured to store a defective address in a nonvolatile manner, and wherein the address specify circuit is configured to selectively invert bits of the bit pattern indicative of bitwise matches or mismatches in response to respective bit values of an output of the memory circuit.
8. The semiconductor memory device as claimed in claim 1 , wherein the address specifying circuit includes:
an address specify circuit configured to specify a first address;
a pattern specify circuit configured to produce an address bit pattern responsive to an externally applied signal; and
a select circuit configured to select, in response to the switchover signal, one of the first address and a second address that is obtained by modifying a value of the first address in response to the address bit pattern produced by the pattern specify circuit.
9. The semiconductor memory device as claimed in claim 8 , wherein the address specify circuit is configured to produce a bit pattern indicative of bitwise matches or mismatches between the first address and an externally applied address in response to selection of the first address by the select circuit, and to produce a bit pattern obtained by selectively inverting respective bits of the bit pattern indicative of bitwise matches or mismatches depending on respective bit values of the address bit pattern in response to selection of the second address by the select circuit.
10. A system, comprising:
a CPU; and
a memory,
wherein the memory includes:
a memory cell array;
a redundant element;
an address specifying circuit configured to select one of a plurality of addresses as a redundancy address in response to a switchover signal;
a decoder circuit configured to select the redundant element in response to an address specified by the CPU that matches the redundancy address selected by the address specifying circuit; and
a test mode setting circuit configured to change the switchover signal in response to instruction from the CPU, thereby to cause the redundancy address assigned to the redundant element to be switched between different ones of the plurality of addresses.