Programmable chip enable for switching and selecting functions to reduce data loading and increase throughput
A memory module includes arrays of memory devices each having a data bus coupled to the data bus of a host memory channel by means of a switching tree. The switching tree is a tree of multiplexers that are controlled to couple the data lines of a single array to the data bus. In some embodiments, a first portion of the chip enable (CE) lines of a memory module are used to enable arrays of memory devices and a second portion are used to control the switching tree. The first portion may control a switching tree coupling the first portion to the enable inputs of the arrays.
1. A memory module comprising:
a DATA bus;
a CE (chip enable) bus;
one or more SW (switch) inputs;
a plurality of memory device arrays, each CE line of the CE bus input being coupled to one array of the plurality of memory device arrays effective to enable the one array in response to asserting of the each CE line; and
a switching tree coupling the DATA bus to data lines of the plurality of memory device arrays, the switching tree being coupled to the one or more SW inputs such that the switching tree connects the data lines of one and only one array of the plurality of arrays to the DATA bus, the one and only one array being determined according to signals on the one or more SW inputs.
2. The memory module of claim 1 , wherein the switching tree is a tree of multiplexers.
3. The memory module of claim 1 , wherein each array of the plurality of memory device arrays includes a plurality of memory chips.
4. The memory module of claim 1 , wherein the DATA bus and the CE bus are connected to contacts arranged according to a dual in line memory module (DIMM) standard.
5. The memory module of claim 1 , wherein the CE bus and the SW inputs are separate from one another.
6. The memory module of claim 2 , wherein the switching tree includes Log 2 (n) levels, where n is a number of the plurality of memory device arrays.
7. The memory module of claim 2 , wherein the multiplexers are analog multiplexers.
8. A memory module comprising:
a DATA bus;
a CE (chip enable) bus;
a plurality of memory device arrays each array having a plurality of data lines for transferring data with the plurality of memory devices and an enable input for permitting access of the each array; and
a first switching tree coupling the DATA bus to data lines of the plurality of memory device arrays, the switching tree being coupled to first lines of the CE bus such that the switching tree defines a path through the switching tree to the DATA bus according to signals on the first lines the path coupling data lines of only a portion of the plurality of memory device arrays that is less than all of the plurality of memory device arrays to the DATA bus;
wherein second lines of the CE bus are coupled to the enable inputs of the plurality of memory devices.
9. The memory module of claim 8 , further comprising a second switching tree coupling the second lines of the CE bus to the enable inputs of the plurality of memory device arrays.
10. The memory module of claim 8 , wherein the first switching tree is a tree of multiplexers.
11. The memory module of claim 8 , wherein the DATA bus and the CE bus are connected to contacts arranged according to a dual in line memory module (DIMM) standard.
12. The memory module of claim 9 , wherein the first lines are coupled to the second switching tree to control the second switching tree.
13. The memory module of claim 10 , wherein the first switching tree includes Log 2 (n) levels, where n is a number of the plurality of memory device arrays.
14. The memory module of claim 10 , wherein the multiplexers are analog multiplexers.
15. The memory module of claim 12 , wherein the second switching tree is configured such that the second lines of the CE bus are coupled only to the enable inputs of the portion of the plurality of memory device arrays according to the signals on the first lines.
16. An apparatus comprising:
a data bus;
a chip enable (CE) bus;
a host memory controller programmed to operate in a first mode with respect to a first array of a plurality of memory device arrays of a first memory module;
wherein the host memory controller is programmed to operate in the first mode by:
asserting a first signal pattern on first lines of the CE bus effective to configure the first memory module to couple data lines of only a subset of the plurality of memory device arrays to the data bus; and
asserting a second line not included in the first lines of the CE bus to enable an array of the subset of the plurality of memory device arrays.
17. The apparatus of claim 16 , wherein the host memory controller is further programmed to operate in a second mode in which a second array of a plurality of memory device arrays of a second memory module connected to the data bus and CE bus is selected by asserting a signal on a line of the CE bus corresponding to the second array and wherein data transfer with the second array is performed over the data bus without altering a path connecting the plurality of memory device arrays of the second memory module to the data bus.
18. The apparatus of claim 4 , wherein multiple lines of the CE bus are not included in the first lines.
19. The apparatus of claim 17 , wherein the DATA bus and the CE bus are connected to pins of a socket according to a dual in line memory module (DENIM) standard.
20. The apparatus of claim 17 , wherein the host memory controller is programmed to assert the first signal pattern on first lines of the CE bus effective to define a path through a switching tree comprising a plurality of multiplexers.