Optimal Memory Tests Coding for Programmable BIST Architecture

Abstract — Programmable memory BIST architecture is becoming a necessity for embedded memory cores. Classical memory BIST architectures use fixed algorithmic tests during the whole live of digital device. To improve the flexibility of memory BIST the programmable solution, based on finite state machine with microcode control, was invented. The requirement to use such flexibility is dictated by reason to use newest test for memory cores. In this paper a new Programmable Memory BIST architecture with small microcode memory is proposed. The analysis of existing March tests allows to code them into the optimal binary format, which cause not only small hardware overhead but also may speed-up the transferring of new test over the serial interfaces like IEEE 1149.1 and P1500. Index Terms — built-in testing, finite state machines, memory testing, microprogramming, random access memories. I. I NTRODUCTION HE progress in system-on-a-chip (SoC) technology makes possible to integrate huge embedded memory cores into a single chip. The testing of embedded memory cores becomes a problem, since they cannot be controlled from the outside by automatic test equipment (ATE). The built-in self-test (BIST) has become an great alternative for embedded memory cores testing [1]. Memory BIST provides high fault coverage, full speed testing, extensive diagnostics instead of expensive and sophisticated ATE. Traditionally BIST is implemented as additional hardware unit, which is an integral part of memory core. Two alternative memory BIST architectures are exist: hardwired memory BIST and programmable memory BIST (P-MBIST). The hardwired BIST customized for a given memory architecture and a predefined set of algorithmic tests. This type of BIST cause low hardware overhead and provides at-speed memory testing. The major disadvantage of hardwired memory BIST architectures is their poor design and functional flexibility. The programmable memory BIST solution provides a certain degree of flexibility to modify test

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