1. A semiconductor memory device having two refreshment modes of auto-refreshment and partial self-refreshment imposed on memory cells, the device comprising:
a command decoder which detects one of the refreshment modes from an input command, outputs type data which indicates the detected refreshment mode, and outputs a refreshment signal which indicates the start of refreshment;
a mode register in which the type data is set;
a signal selection circuit which determines whether or not the refreshment signal is to be delayed, in accordance with the type data set in the mode register, and outputs the refreshment signal, which is delayed or not delayed in accordance with the result of the determination, as a refreshment start signal; and
a control circuit which reads the type data set in the mode register based when receiving the refreshment start signal, and performs refreshment corresponding to the type data.
2. The semiconductor memory device in accordance with claim 1, wherein:
when the type data indicates the auto-refreshment, the signal selection circuit outputs the non-delayed refreshment signal as the refreshment start signal; and
when the type data indicates the partial self-refreshment, the signal selection circuit outputs the delayed refreshment signal as the refreshment start signal.
3. The semiconductor memory device in accordance with claim 2, wherein:
the signal selection circuit has a delay time used when the type data indicates the partial self-refreshment, by which the refreshment signal is output as the refreshment start signal after the output of the refreshment signal from the command decoder is completed.
4. The semiconductor memory device in accordance with claim 1, wherein the signal selection circuit includes:
a delay part for delaying the refreshment signal; and
a selection part for determining whether the delayed refreshment signal, which has been delayed by the delay part, or the non-delayed refreshment signal, which has not passed through the delay part, is to be output in accordance with the type data.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A process for synthesis of a graft copolymer comprising grafting:
a copolymer (II) obtained from the copolymerization of a first monomer comprising styrene or derivatives thereof and a second monomer comprising at least one anhydride function,
with molecules M-R-X (I) comprising a nitrogen-containing heterocyclic group (M) selected from the group consisting of units (1) to (4):
with A=oxygen,
R is a hydrocarbon chain, and (X) is selected from a halogen, a thiol function, and an epoxy function,
wherein the graft copolymer comprises more than two grafts per chain of the copolymer.
2. The process according to claim 1, wherein the copolymer (II) is obtained from the copolymerization of a mixture of monomers containing by weight, relative to the total mixture of monomers, between 0.5% and 50% of monomer comprising an anhydride function.
3. The process according to claim 1, wherein the monomer comprising an anhydride function is maleic anhydride.
4. The process according to claim 1, wherein the heterocyclic group (M) of the molecule (I) is the unit (1).
5. The process according to claim 1, wherein (R) is a linear or branched alkyl chain composed of one to 30 carbon atoms.
6. The process according to claim 5, wherein (R) has a molecular mass of less than 1000 gmol.
7. The process according to claim 2, wherein the copolymer (II) is obtained from the copolymerization of a mixture of monomers containing by weight, relative to the total mixture of monomers, between 15% and 30%, of monomer comprising an anhydride function.
8. The process according to claim 1 wherein (R) has a molecular mass of less than 500 gmol.
9. A graft copolymer comprising:
a copolymer (II) grafted with molecules M-R-X (I) comprising a nitrogen-containing heterocyclic group,
the copolymer (II) obtained from the copolymerization of a first monomer comprising styrene or derivatives thereof and a second monomer comprising at least one anhydride function,
the molecules M-R-X (I) comprising a nitrogen-containing heterocyclic group (M) selected from the group consisting of units (1) to (4):
where A=oxygen, R is a hydrocarbon chain, and X is selected from a halogen, a thiol function, and an epoxy function,
and the graft copolymer comprises more than two grafts per chain of the copolymer.
10. The graft copolymer of claim 9, wherein the unit (M) of the molecule (I) is the unit (1).
11. The graft copolymer of claim 9, wherein the chain (R) is a linear or branched alkyl chain composed of one to 30 carbon atoms.
12. The graft copolymer of claim 9, wherein the chain (R) has a molecular mass of less than 1000 gmol.