SPI : changing CS pin

Allison K

Has anyone succeeded in changing the pins used for SPI from the default (MISO = 9; MOSI = 8; CLK = 7; CS1 = 6). I'm mainly interested in changing the CS1 pin setting. I have multiple SPI devices and I want to disable/enable to select one at a time.

The SPI devices I am using are active-low enable. I am using an Omega 2+.

Here's the setup code I'm using (python):

# GPIO.output(pinNumber=6, setting=GPIO.HIGH)
# GPIO.output(pinNumber=18, setting=GPIO.LOW)

...
LSBFIRST = 1

busNumber = 1
deviceId = 32766
...
self.device = onionSpi.OnionSpi(busNumber, deviceId)
...
spi.sck =  7
spi.mosi = 8
spi.miso = 9
spi.cs = 18
# spi.noCs = 1
# spi.csHigh = self.csHigh
self.set_bit_order(LSBFIRST)

# check the device
if spi.checkDevice() is 0:
            mapped = "the device adapter is already mapped."
else:
            mapped = "the device adapter is NOT mapped."
print("Registered: {}".format(mapped))

# register the device
if spi.registerDevice() is 0:
            success = "Device with the specified bus number and device ID is already registered OR successfully registered SPI device adapter."
else:
            success = "Unable to register device."
print("Registering.. : {}".format(success))

# initialize the device parameters
if spi.setupDevice() is 0:
            success = "Setup successful."
else:
            success = "Setup failed."

print("Setting up spi device: {}".format(success))

# check the device again
if spi.checkDevice() is 0:
            mapped = "the device adapter is already mapped."
else:
            mapped = "the device adapter is NOT mapped."
print("Registered: {}".format(mapped))

### Here I print out all the parameters of the OnionSpi object

What I am seeing:

pin6 is always high (though the SPI device is read fine using the above setup code).
when manually changing GPIO value using something like the commented code at top : GPIO 18 switches low-to-high or high-to-low correctly, but when setting pin 18 as CS pin, nothing happens (no value change, ever). [the manual change of pin18 in conjunction with the noCS option commented out in above code]
Setting the csHigh value to one (in commented code) doesn't seem to have any effect whether cs pin is set to 6 or 18
I have confirmed that the SPI variables regurgitated after registration match the changes (pin 18 set to cs). See below.

Registered: the device adapter is already mapped.
> SPI device already available
Registering.. : Device with the specified bus number and device ID is already registered OR successfully                         registered SPI device adapter.
> Initializing SPI parameters...
  > Set SPI mode:       0x508
  > Set bits per word:  0
  > Set max speed:      100000 Hz (100 KHz)
Setting up spi device: Setup successful.
Registered: the device adapter is already mapped.
----------------
SPI Device Settings:
  bus:    1
  device: 32766
  speed:    100000 Hz (100 kHz)
  delay:    0 us
  bpw:      8
  mode:     0 (0x08)
     3wire:    0
     lsb:      1
     loop:     0
     no-cs:    0
     cs-high:  0

GPIO Settings:
  sck:      7
  mosi:     8
  miso:     9
  cs:       18 

----------------

Any hints on how to debug this would be greatly appreciated. Thanks!

Related links:
Communicating with SPI devices
SPI Python module

Jaime Cerecer

Hello Allison,
Were you able to connect more SPI devices? Could you share your experiences? I am asking you because I am planning to connect 3-4 SPI devices with high sampling rate (>40kHz) and I will need to use other GPIO to do it in parallel

Jeremy Shubert

Was this resolved? I am planning to have 4-5 devices on SPI and will need to be able to set up different CS lines.

Jaime Cerecer

@Jeremy-Shubert I am still fighting with it... have you been able to communicate with at least one device? I am having issues to read the bytes...