G400 - Multiple SPI CS

NETMF & Gadgeteer
1

Hello,

New to the forum, still getting the hang of things with the G400. I am trying to use the SPI2 module on the G400 to access multiple IC’s. Now, the way that my circuit has been set up is to use a MUX that will select between which IC CS pin to access. I managed to get the SPI to work when I set a specific pin on the G400 but I am not sure how to tell the SPI communication protocol which switch case I would like to use if I implement the MUX. Any suggestions?

Thank You,
Dave




// Digital Potentiometer 
            // CS - Use MUX table, up to eight options

        static  OutputPort DIG_POT_EN = new OutputPort(GHI.Pins.G400.PD8, true); // bool true will set all CS to high
        static  OutputPort DIG_POT_S0 = new OutputPort(GHI.Pins.G400.PC23, true);
        static OutputPort DIG_POT_S1 = new OutputPort(GHI.Pins.G400.PD0, true);
        static  OutputPort DIG_POT_S2 = new OutputPort(GHI.Pins.G400.PD2, true);
 
public static void Main()
        {
            int chann = 2;
            SPI.Configuration SPI_DigPot = new SPI.Configuration(?????,  //Chip Select Port
               false, //ChipSelect Active State
               0,     //CLK Setup Time
               0,     //CLK Hold Time
               false, //Clock Idle State
               false, //Clcok Edge
               400,   //Clock Rate kHz
               SPI.SPI_module.SPI2); //SPI Module
            

            ushort[] Wiper_Pos_EN   = new ushort[] { 0x0500 };   // Enable update of wiper positons
            ushort[] Wiper          = new ushort[] { 0x1802 };   // Wiper Position
            ushort[] RDAC_Read      = new ushort[] { 0x0800 };   // Prepare data read from RDAC register
            ushort[] NOP            = new ushort[] { 0x0000 };   // NOP instruction

            
            MySPI.WriteRead(Wiper_Pos_EN, rx_data); //send data
            DIG_POT_EN.Write(true); //set all CS to high 
           
        }
        private void Update_Wiper_Channel(int DIG_POT_Channel)
        {
            switch (DIG_POT_Channel)
            {
                case 1: //Channel 1 Digital Pot CS is selected
                    DIG_POT_EN.Write(false);
                    DIG_POT_S0.Write(false);
                    DIG_POT_S1.Write(false);
                    DIG_POT_S2.Write(false);
                    break;

                case 2: //Channel 2 Digital Pot CS is selected
                    DIG_POT_EN.Write(false);
                    DIG_POT_S0.Write(true);
                    DIG_POT_S1.Write(false);
                    DIG_POT_S2.Write(false);
                    break;

                case 3: //Channel 3 Digital Pot CS is selected
                    DIG_POT_EN.Write(false);
                    DIG_POT_S0.Write(false);
                    DIG_POT_S1.Write(true);
                    DIG_POT_S2.Write(false);
                    break;

                case 4: //Channel 4 Digital Pot CS is selected
                    DIG_POT_EN.Write(false);
                    DIG_POT_S0.Write(true);
                    DIG_POT_S1.Write(true);
                    DIG_POT_S2.Write(false);
                    break;

                case 5: //Channel 5 Digital Pot CS is selected
                    DIG_POT_EN.Write(false);
                    DIG_POT_S0.Write(false);
                    DIG_POT_S1.Write(false);
                    DIG_POT_S2.Write(true);
                    break;

                case 6: //Channel 6 Digital Pot CS is selected
                    DIG_POT_EN.Write(false);
                    DIG_POT_S0.Write(true);
                    DIG_POT_S1.Write(false);
                    DIG_POT_S2.Write(true);
                    break;

                case 7: //Channel 7 Digital Pot CS is selected
                    DIG_POT_EN.Write(false);
                    DIG_POT_S0.Write(false);
                    DIG_POT_S1.Write(true);
                    DIG_POT_S2.Write(true);
                    break;

                case 8: //Channel 8 Digital Pot CS is selected
                    DIG_POT_EN.Write(false);
                    DIG_POT_S0.Write(true);
                    DIG_POT_S1.Write(true);
                    DIG_POT_S2.Write(true);
                    break;
                default:
                    break;
}
}
2

I believe in the setup of the SPI.Configuration you can pass in null for the CS port pin but if not, pass in an unused pin.

Before you call the SPI routine to read or write, simply call your function that sets the CS pin and after the read or write, de-assert the CS.

3

Use multiple Spi configs with the required CS pins.

Then set the required config for spi.

Rinse and repeat.

4

That doesn’t work in this case Justin as he uses a MUX to select the device, hence the case statements. There is no GPIO on the CPU to select the CS on each device.