AN-136

www.DataSheet4U.com A NEW GENERATION OF TAG SRAMS—THE IDT71215 AND IDT71216 Integrated Device Technology, Inc. APPLICATION NOTE AN-136 By Kelly Maas INTRODUCTION The 71215 and 71216 represent a new generation of integrated Tag SRAMs. Just as earlier Tag SRAMs such as the 71B74 were better suited for tag applications than conventional SRAMs, the 71215/16 go a step further by integrating new features to significantly ease the design of high performance cache subsystems for today’s high speed processors. These Tag RAMs are designed for easy interfacing to Intel and PowerPC processors, but are very flexible and can easily be used in other applications as well. This application note first provides some background information on caches, then describes in detail the architecture and operation of the 71215 and 71216. This is followed by three application examples, then a brief discussion of cache coherency protocol implementation using these Tag RAMs. Since the 71215 and 71216 are very similar, the descriptions and explanations in this application note apply to both unless otherwise noted. CACHE AND TAG BASICS For those new to caches, a brief review of cache basics may be worthwhile. A cache is a memory that provides a CPU with high speed access to a subset of the data from main memory. Our discussions are focused on the secondary cache, which is also known as the L2 cache, but it is not much different from the faster primary (L1) cache residing inside most CPUs. The cache consi...