POY6.JAN–MUSIC Semiconductors–RM
Content-addressable memory returns associated data
The MU9C1640 CacheCAM is a content-addressable memory (CAM) with a novel organization that makes fully associative caches and data-search engines much simpler than current techniques would allow. Within its capacity, the device can return actual data on a match, not just a pointer, as would an normal CAM. Its 1,024 lines of 64 bits may be divided on 16-bit boundaries into CAM and RAM sections, making a fully associative cache on one chip. For example, a successful search on the first 16 bits could return 48 bits of data immediately, without accessing separate static memory. Applications include virtual memory, caches, content-searching database machines, and image processing.
Synchronous control logic, along with status flags, allow glueless vertical cascading. The full (FF) and match (MF) flags of the last device in the chain act as system-full and system-match flags for the whole string (see diagram). FF feeds FI and MF feeds MI on intermediate devices. Thus the cascade acts just like a single device, except that it has greater capacity.
Two mask registers can mask writes and compares. For compares, the mask determines which bits of the comparand are to be compared with the contents of valid locations. A priority encoder resolves multiple matches.
A page-address register is loaded at startup with upper address bits. During a compare cycle, the 10 low bits of the match address append to the high address bits of the page-address register to produce a system match address.
The part supports three kinds of memory cycle: associative access, random access, and write to next free address. Each 64-bit line has a pair of extra CAM bits that indicate valid data, skip, empty, and random-access-only.
The internal 64-bit data path is multiplexed to a 16-bit external port, to get the device into an economical 44-pin PLCC package. Two speed grades have 55- and 40-ns write cycles (MU9C1640-40, $ 32.50 ea/1,000–available now.)
MUSIC Semiconductors
Colorado Springs, CO
Information 800-788-MUSIC
CAPTION:
Each 64-bit line of the memory array can be divided into content-addressible and associated data portions.
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