I was just wondering. I am doing this thing with a Max7221 and i am just learning about SPI.
On the arduino i am only capable of having one SPI connection right?
Hi,
the number of SPI devices you can control from an arduino, depends depends on the hardware you want to control.
For 8 MAX7221 you only need a single SPI-connection, so it is possible with this chip.
There is a lot of information here
http://www.arduino.cc/playground/Main/LEDMatrix
Eberhard
It is like saying I have only got 19 pins on the arduino so I can only control 19 digital signals.
You can control as many SPI devices as you want, all you have to do is to sort out the enabling of the one device you want to talk to at any one time. This can be done inside the device, if it offers and address structure or externally by routing chip enables controlled from other I/O chips.
The max7221 can be serially connected to one another also-
You can use as many as you like. The atmega on the arduino will run out of pins at some point. Then use an output expander so you can get more chip select lines and keep going. Unfortunately SPI requires a chip select line for every chip and it will quickly eat up all the I/O on a small microcontroller. Use something like a 595 serial in, parallel out shift register to control which SPI chip you want to talk to. You can even use the 595 to control the SPI data channels which will free up more I/O on the arduino.
Unfortunately I have not had the time to make this work. It is far more involved in the low level code of the atmega chip than the arduino normally handles.