Driving SPI Ports
Posted 28 February 2013 - 09:45 AM
Posted 28 February 2013 - 01:16 PM
Posted 01 March 2013 - 08:20 AM
2. Use 3 digital I/O to provide CLK/MISO/MOSI, and then use 1 digital output for each device to control CS. This lets you talk to up to 17 devices.
The potential issue with the latter technique, is the the 3 CLK/MISO/MOSI lines are connected to 18 devices at the same time. 1 device is driving the line, while 17 devices are set to high-impedance input mode. If the impedance of the 17 devices is too low, or the capacitance is too high, you can have communication problems. With standard logic, I would not expect impedance or capacitance to be a problem. Two recommendations:
- Use EIO or CIO lines for CLK/MISO/MOSI, as they have less impedance than FIO lines.
- If you have too much capacitance (rise and fall times are too slow), you can use SPI_CLOCK_FACTOR to slow down the SPI data rate.
I was planning to do that. Use 3 I/o Lines for SPI and I have a multiplexer to control the CS lines. I was just wondering if the Digital I/O could drive 8 lines for my devices.
0 user(s) are reading this topic
0 members, 0 guests, 0 anonymous users