More than 2 SPI slaves

[pmueller]

Hello,

I like to connect more than two SPI slaves to the Raspberry.
Unfortunately there are only to chip select pins possible (/CS0, /CS1). I can use GPIO pins for all of the SPI slaves, but then I can't use /CS0 and /CS1 anymore.

I looked into the kernel sources and saw that there seems to be the possibility to define not using any chip select. But control the the chip select via port pins in the application. But this seems not to work (at least what I tried).

Has anyone more than 3 SPI devices running that way?

Thanks,
Peter

[TheRayTracer]

You may successfully use more that two SPI style devices. You may simply use any free GPIO pin on the RPi to manually toggle the CS for the slave device. This may not work for all SPI devices, such as those that require the CS to go inactive between each byte of a transmission, but most devices would have no issue with using this method.

[brekee12]

There is an additional auxilary SPI on B+ Zero 2B which is located on the header and have three CS. This is additional to the standard SPI, but separate handling by sofware. Study joan's pigpio library which makes the handling. Very usefull option!

[adun]

The current spi-bcm2835 driver supports additional GPIO chip-selects. For driver performance the hardware chip-select pins (CE0,CE1) will be automatically converted to GPIO CS's pins.

[thomen]

Just wondering if anyone has done anything with more than 2 slaves using daisy chaining or the like?
I'm looking to wire up around 6 colour oleds using SPI

[brekee12]

As I mentioned auxilary SPI available on B+, 2B, Zero has three CE.

[blushi]

Just wondering if anyone has done anything with more than 2 slaves using daisy chaining or the like?
I'm looking to wire up around 6 colour oleds using SPI

I did actually. See my post: viewtopic.php?p=940975#p940975 (even though I am facing now some issues, you can get the idea ) If you have any further questions, I'd be glad to help.

[mikronauts]

http://www.mikronauts.com/raspberry-pi/ ... and-howto/

Shows you how to generate eight chip selects from one...

[thomen]

I was hoping to Daisy chain 6 oled small screens. Do you think that would be possible??

[thomen]

Wow micronaughts I can't even begin to understand half of what you've written! (Being totally green and all) time to Google like crazy and read electronics for dummies ha-ha..

[mikronauts]

Hi.

You can't daisy chain SPI, as each device needs its own chip select.

You can daisy chain i2c.

The circuit in my article basically adds a "one of eight" de-multiplexer, and uses that to generate individual chip selects from a three bit binary number, and one of the chip selects on the GPIO connector.

[thomen]

Thanks !
I'll give it a try! I wanted to try and run up to 6 oleds with a pi

[crishoj]

Are you certain that daisy-chaining on SPI is not possible?

Daisy-chaining with a single, shared chip-select seems to be a common mode of operation. See e.g. http://www.petervis.com/Raspberry_PI/SP ... Chain.html

[joan]

Are you certain that daisy-chaining on SPI is not possible?

Daisy-chaining with a single, shared chip-select seems to be a common mode of operation. See e.g. http://www.petervis.com/Raspberry_PI/SP ... Chain.html

That does not make sense. I suggest you contact the author and ask for clarification. He may have a very specialised use with one model of chip in mind.

[crishoj]

Of course, the SPI devices in a chain would have to support daisy-chaining, namely by re-transmitting their input to the next device on the following clock cycle.

See here for a description:
https://en.wikipedia.org/wiki/Serial_Pe ... figuration

Typical wiring, with one chip-select per device:


Daisy-chain wiring, with a single, shared chip-select:

[crishoj]

Here is a specific example of chaining 3 AutoDrivers:
http://www.deathbylogic.com/2015/01/dai ... todrivers/

Data is shifted down the chain:

The way daisy chaining works with multiple devices on a single SPI bus is similar to shift registers, data from the SPI master is shifted out MSB first and shifted into the SPI slave on the falling edge of the SPI clock. At the same time the data in the slave is shifted out to the next device, when there is only a single slave device this would go back to the MISO pin on the master or with multiple slave devices the MOSI pin on the next slave. The number of devices that can be daisy chained together is only limited by length of the SPI bus and delay caused by each of the SPI devices on the SPI bus

Illustration:


And here is a more technical description of the daisy-chaining SPI:
https://www.maximintegrated.com/en/app- ... vp/id/3947

I will be attempting a chained setup with 6 AutoDrivers in the coming weeks, and will be happy to report back how it goes.

[joan]

It's simpler just to use shift registers to implement shift registers.

I don't remember any posts where SPI daisy chaining has actually being used on the Pi.

[peter.shea]

chrishoj:

I will be attempting a chained setup with 6 AutoDrivers in the coming weeks, and will be happy to report back how it goes.

Did you ever get this working?

[OutoftheBOTS]

There is a second SPI bus that has another 3 CS pins see http://terminal28.blogspot.com.au/2016/ ... ero23.html
but also I found that to make room on the broad com chip you need to remove the Bluetooth or the serial console. I removed the serial console to use the SPI bus 1

[SteveA]

Peter, from your original post, would you mind letting me know how you can disable the kernel from toggling CE0 or CE1 when using SPI because if that is what I have been trying to find out,
Thanks in advance
Steve