存储器的类型将决定整个嵌入式系统的操作和性能,因此存储器的选择是一个非常重要的决策。无论系统是采用电池供电还是由市电供电,应用需求将决定存储器的类型(易失性或非易失性)以及使用目的(存储代码、数据或者两者兼有)。另外,在选择过程中,存储器的尺寸和成本也是需要考虑的重要因素。 根据存储器在计算机系统中所起的作用,可分为主存储器、辅助存储器、高速缓冲存储器、控制存储器等。为了解决对存储器要求容量大,速度快,成本低三者之间的矛盾,目前通常采用多级存储器体系结构,即使用高速缓冲存储器、主存储器和外存储器。 FEATURES · +3.3 Volt power supply · Fast 35 ns read/write cycle · SRAM compatible timing · Unlimited read & write endurance · Data always non-volatile for >20 years at temperature · RoHS-compliant small footprint BGA and TSOP2 package INTRODUCTION The MR4A16B is a 16,777,216-bit magnetoresistive random access memory (MRAM) device organized as 1,048,576 words of 16 bits. The MR4A16B offers SRAM compatible 35 ns read/write timing with unlimited endurance. Data is always non-volatile for greater than 20 years. Data is automatically pro-tected on power loss by low-voltage inhibit circuitry to prevent writes with voltage out of specification. To simplify fault tolerant design, the MR4A16B includes internal single bit error correction code with 7 ECC parity bits for every 64 data bits. The MR4A16B is the ideal memory solution for applications that must permanently store and retrieve critical data and programs quickly. The MR4A16B is available in a small footprint 48-pin ball grid array (BGA) package and a 54-pin thin small outline package (TSOP Type 2). These packages are compatible with similar low-power SRAM products and other nonvolatile RAM products. The MR4A16B provides highly reliable data storage over a wide range of temperatures. The product is offered with commercial temperature (0 to +70 °C), and industrial temperature (-40 to +85 °C) operating temperature options.