Contents
What kind of resistors should I use for long SPI bus lines?
2k2 may work with 10kHz, with 1MHz you need a smaller value – the higher the resistor value the slower are the signal edges (caused by RC, where C is the capacitance of the long wire). Use something like 50-220ohm with ~xMHz SPI frequencies.
How can I solve the problem of SPI?
I want to connect chips that use SPI protocol to communicate (To be specific those chips are ws2801) the distance may reach 100 meters. How can I solve this issue?
How are peripherals connected to the SPI bus?
There are two ways of connecting multiple peripherals to an SPI bus: In general, each peripheral will need a separate CS line.
What happens if you look at the wrong time on SPI?
If the receiver is looking at the wrong times, it will see the wrong bits. SPI works in a slightly different manner. It’s a “synchronous” data bus, which means that it uses separate lines for data and a “clock” that keeps both sides in perfect sync.
Which is the fastest signal for the SPI bus?
Apparently that is not quite enough and/or is not predictable enough. This can be fixed with some deliberate capacitance on each line. You want to run the bus at 4 MHz, which means the fastest signal it needs to support is a 4 MHz square wave.
What should the ground clip be for SPI bus termination?
Probing anywhere else will likely give you a distorted waveform and trick you into thinking that things are worse than they really are. Also, make sure that your ground clip is as short as possible. Conclusion: Switch to source termination with a 33 to 50 ohm resistor and you should be fine. The usual caveats apply.
What should the hidden capacitance be on a SPI bus?
That leaves room for 10-20 pF of hidden capacitance while not exceeding our maximum allowed time constant. The series resistors should be as close as possible to all pins that drive the bus. This assumes that all other pins on the bus will be CMOS inputs when one is driving.