在数据采集、过程监测与自动记录、自动化仪器仪表等领域,经常需要对采集的数据、运行的状态以及计算的中间结果等采取必要的保护措施,以防止由于供电系统突然断电导致信息的丢失。对于造价较高的微机系统,可采用不间断电源(UPS)对系统进行一定时间的保护,但对于需长时间保存RAM中的信息,上述方法已不适用,这时可以采用后备电池给RAM供电,从而保护必要的内容。微型计算机主机使用的RAM可分为两大类,一类是动态随机存贮器(DRAM),另一类是静态随机存贮器(SRAM)。DRAM工作时需要时时对其内容刷新,否则信息就丢失。一般说来,刷新信号来自CPU,这样要使DRAM的内容不丢失,不仅要给DRAM供电,而且还要使系统不断电,显然耗电大,不宜用后备电池保护。SRAM的内容在微机工作时不需要刷新,只要其电源电压不掉电就可以长久保持。对于CMOS静态RAM来说,在静态时消耗的电流仅是微安级,若采用常用的5号电池,也可以给CMOS静态RAM供电两年以上。由于CMOS电路工作可靠、耗电省、可以方便地与TTL电路匹配,而且用电池供电成本低,更换方便,所以下面介绍经常使用的几种CMOS静态RAM的掉电保护的方法。 In the fields of data acquisition, process monitoring and automatic recording, and automated instrumentation, it is often necessary to take necessary protective measures against collected data, operating status and calculated intermediate results to prevent the loss of information due to a sudden power failure of the power supply system . For the high cost of the computer system, you can use the uninterruptible power supply (UPS) to protect the system for some time, but for a long time to save the information in RAM, the above method does not apply, then the backup battery can be used to power RAM , Thus protecting the necessary content. Microcomputer mainframe RAM can be divided into two categories, one is dynamic random access memory (DRAM), the other is static random access memory (SRAM). DRAM work needs to refresh its content, or the information is lost. In general, the refresh signal from the CPU, so that the content of the DRAM is not lost, not only to the DRAM power supply, but also to make the system uninterruptible power supply, apparently large power consumption, should not be backed up with battery protection. The contents of the SRAM do not need to be refreshed when the microcomputer is working, as long as the power voltage of the SRAM can be maintained for a long time without power failure. For CMOS static RAM, the current consumed in the static state is only a micro-ampere level. If the commonly used 5-cell battery is used, the CMOS static RAM can also be powered for more than two years. Due to the reliable operation of the CMOS circuit and the low power consumption, it can be conveniently matched with the TTL circuit, and the cost of the battery is low and the replacement is convenient. Therefore, several methods for power-down protection of the CMOS static RAM that are often used are described below.