串行存储器.docx

外文翻译Serial MemoriesOverviewMany of us like to use small, single chip micro controllers. They are relatively cheap, easy to wire up to make run, and over all just mighty convenient to use. One down side to using these single chip controllers is the lack of large amounts of memory. Sure, you can hook up external memory to most of them, but that requires a lot of work, and usually consumes other valuable resources, mainly the I/O pins that make the chip useful.There is help out there! There are several forms of memory that dont require the standard address bus and data bus wiring. These memories are called serial memories, and they are just the ticket to allow you to store large amounts of information without giving up those precious I/O lines. There are several different styles of serial EEPROM. The focus of this article is going to be SPI based devices. There are also 1, 2, and 3 wire serial EEPROM devices that function in a similar way, but have different interface logic.This article is going to introduce the basics of serial memories, and present the driver software needed to make it operate.Missing the BusThe big advantage to using a Serial EEPROM is that the wiring only requires 4 signal lines from the CPU to operate it. Compare this with a more standard memory, which requires an address bus and a data bus! The amount of glue logic required to make a Serial EEPROM operate is extremely low. For example, check out the following two packages. A traditional memory, such as a 27256, requires a 28-pin part to be wired into your circuit. There are 15 address lines, 8 output lines, plus assorted control lines. On the other hand, a serial EEPROM can be purchased using in a 8-pin package. There is 1 input line, 1 output line, 1 control line, and 1 clock line required. There are a couple of other control lines available, but are not actually required if you wish to avoid them. As you can imagine, these parts a lot easier to wire in, much smaller and best of all are mighty c