翻译资料1——SPI访问.doc

串行外围接口SPI的访问 作者：Siri Namtvedt 关键字： ? CC1100 ? CC1101 ? CC1150 ? CC2500 ? CC2550 ? SPI ? 复位 突发访问 ? 命令滤波 1 简介 本设计说明的目的是让我们了解该如何配置SPI接口使其能够与CC1100/CC1101/CC1150/CC2500/CC2550连接，并且告诉我们要如何理解状态字节，以及复位开关在SPI接口上是怎么实现的，另外也描述了我们可以使用的不同SPI接口的访问（读/写,单址访问/突发访问以及命令滤波）。 目录 简介·····································································1 缩写词···································································3 SPI接口·································································3 SPI接口配置·······················································3 SPI接口的时间要求·················································4 SPI的访问·························································4 单字节访问·························································5 突发访问···························································5 命令滤波···························································5 芯片的状态字节···························································7 复位·····································································9 总说明···································································10 2 缩写词 MCU 微控制器单元 SPI 串行外围接口 3 SPI接口 CC1100/CC1101/CC1150/CC2500/CC2550的接口配置为一个简单的4线SPI兼容接口(SI, SO, SCLK和CSn)，在这里无线电受到MCU的控制。这个接口也可以同时用作写或读缓存数据。在SPI接口上传输的所有地址和数据都要在最重要的位上先进行。 SPI接口配置 配置时要注意连接MCU的SPI接口必须在主模式下操作。配置时钟相位时要确保数据的中心在SCLK周期的第一个正边缘处，在选择极性时要确保SCLK在静止状态时为低电平。 SPI接口的时间要求 关于SPI接口的时间要求，详情请查看芯片数据表。值得注意的是最大SCLK频率(fsclk)是如何改变的，这主要取决于SPI接口的使用情况。SPI时钟运行的最大频率是10 MHz，在地址字节和数据字节（单字节）之间、地址和数据之间或者每一个数据字节之间（突发访问）的最小延迟是100ns。如图3所示。 如果各字节之间没有延迟，那么单通道的最大时钟速度是9MHz（图4），突发访问为6.5MHz（图5）。 SPI的访问 芯片上有47个配置寄存器（地址0000至地址0x2E）。寄存器的读写操作由头地址的R/W位控制，而burst突发访问位控制访问方式为单字节还是突发访问。 图6 头地址 当CSn变低，我们总是要等到MISO(CHIP_RDYn)变为低电平之后再进行头地址的写操作。CHIP_RDYn信号表明晶体正在运行，调节数字供给电压是稳定的。只要芯片不是在SLEEP或XOFF状态或者一个SRES闪光灯发出命令的情况下，SO引脚总是在CSn变成低电平之后也迅速变为低电平。 图7 图7显示了电磁波从IDLE (1)静止状态转变为SLEEP休眠状态(SPWD)，接着通过发射一个TX滤波(STX) (2)使其在休眠状态后被唤醒的工作过程。当CSn变为低电平时电磁波从休眠状态中唤醒。在CSn首次变为低电平时，MISO变为高电平，然后又