| abstract |
Phase-change memory (PCM) cells store data using alloy resistors in high-resistance amorphous and low-resistance crystalline states. The time of the memory cell's set-current pulse can be 100 ns, much longer than read or reset times. The write time depends on the write data state and is relatively long for set, but short for clear. A PCM chip has a lookup table (LUT) caching write data that is later written to a PCM bank. Host data is latched into a line FIFO and written into the LUT, reducing write delays to the slower PCM. The PCM chip has upstream and downstream serial interfaces to other PCM chips arranged as a token stub. Requests are passed down the token-stub while acknowledgements are passed up the token-stub to the host's memory controller. Shared chip-enable lines are driven by the upstream PCM chip for requests, and by the downstream PCM chip for acknowledgements. |