Hi Terry, > > OLED_RST_PIN = 25 > > OLED_DC_PIN = 24 > > OLED_CS_PIN = 8 > > It's the OLED_CS_PIN (and possibly the OLED_DC_PIN) that I will > probably want to manage.
I'd assume reset and data/command are gated as inputs to each SPI device on the bus by the chip-select line so D/C doesn't need switching to each device, just CS. But I'd examine the data-sheet of the SPI device in question to seek confirmation. > I had misunderstood that when I looked at this previously and assumed that > SPI0 and SPI1 on the Pi GPIO Pins referred to two discrete buses which could > then have 1 to n devices attached and selected by the CS lines. > > I can see that I can obviously have two devices attached, based on the above, > but more than two might mean a bit more hoop-jumping, assuming it's available > at all. https://www.raspberrypi.org/documentation/hardware/raspberrypi/spi/README.md says The Raspberry Pi is equipped with one SPI bus that has 2 chip selects. so I'm assuming there's not another SPI bus which isn't normally enabled or allocated pins. But that seems to contradict with https://pinout.xyz/pinout/spi which shows SPI0: SCLK MOSI MISO CE0 CE1 SPI1: SCLK MOSI MISO CE0 CE1 CE2 as if there's two buses with three chip-select lines on the second one. Perhaps I'm misunderstanding the diagram. Could you demux outputs from the Pi to give more chip-selects lines, e.g. four GPIOs could drive one of 2⁴=16 CS lines. https://en.wikipedia.org/wiki/Demux#Digital_demultiplexers It's the demux's outputs which fan off as CS to each SPI device. Meanwhile, they all get SCLK, MOSI, RST and D/C straight from the Pi. You could leave the software thinking there was only one SPI device and drive the demuxer yourself just before each run of SPI-writing for a device. If they were different speed devices then you'd have to change the bus speed too. No idea if it would work. This is a hardware problem. :-) It seems it is possible. https://forum.pjrc.com/threads/34666-16-SPI-devices-Is-it-possible An I²C port expander to drive 16 CS is an alternative to the 4-to-16 demux. -- Cheers, Ralph. -- Next meeting: Online, Jitsi, Tuesday, 2020-09-01 20:00 Check to whom you are replying Meetings, mailing list, IRC, ... http://dorset.lug.org.uk New thread, don't hijack: mailto:dorset@mailman.lug.org.uk
