If you're using the SPI Library, you must use the provided SCK, COPI and CIPO pins, as the hardware is hardwired to those pins. In the Arduino SPI library, the speed is set by the setClockDivider() function, which divides the controller clock (16MHz on most Arduinos) down to a frequency between 8MHz (/2) and 125kHz (/128).
To accommodate such devices, you can adjust the data rate. SPI can operate at extremely high speeds (millions of bytes per second), which may be too fast for some devices. In the Arduino SPI library, both of these options are controlled by the setDataMode() function.
Additionally, the clock can be considered "idle" when it is high or low. The peripheral will read the data on either the rising edge or the falling edge of the clock pulse. In the Arduino SPI library, this is controlled by the setBitOrder() function. The interface can send data with the most-significant bit (MSB) first, or least-significant bit (LSB) first. These options must match those of the device you're talking to check the device's datasheet to see what it requires. You will need to select some options when setting up your interface. This is vastly faster than the above commands, but it will only work on certain pins. Or you can use the SPI Library, which takes advantage of the SPI hardware built into the microcontroller. These are software-based commands that will work on any group of pins, but will be somewhat slow. You can use the shiftIn() and shiftOut() commands.
If you're using an Arduino, there are two ways you can communicate with SPI devices: (A good example is on the Wikipedia SPI page.) The SPI protocol is also simple enough that you (yes, you!) can write your own routines to manipulate the I/O lines in the proper sequence to transfer data. Many microcontrollers have built-in SPI peripherals that handle all the details of sending and receiving data, and can do so at very high speeds. Share on Twitter Share on Facebook Pin It Programming for SPI
0 kommentar(er)
