Hardware SPI - Simple demo. Writing and reading data.

[Roger Jönsson]

Here is a an easy to understand example sending and receiving data over Hardware SPI.
I needed something to test on, so I took a RAM (chip 23LCV1024 1Mbit) and after som hair loss, I had managed how to write data on to it, verifying by reading the data back. I hope it will be useful to someone else.

#CHIP 18F27Q84, 64
#OPTION Explicit


    #include <glcd.h>
    #DEFINE GLCD_TYPE         GLCD_TYPE_SSD1306
    #DEFINE GLCD_I2C_Address  0x78 
    // Define I2C Software settings
    #DEFINE I2C_MODE Master
    #DEFINE I2C_DATA    PORTC.0
    #DEFINE I2C_CLOCK   PORTC.1
    #DEFINE I2C_DISABLE_INTERRUPTS ON
    GLCDPrint (0, 0, "i2C GLCD TEST")


    // PIC PPS Tool version: 0.0.6.5
    #startup InitPPS, 85
    #define PPSToolPart 18F27Q84
    Sub InitPPS        
            // Module: SPI1
            SPI1SDIPPS = 0x0016   // RC6 > SDI1
            RC5PPS = 0x0032       // SDO1 > RC5
            RC4PPS = 0x0031       // SCK1 > RC4
            SPI1SCKPPS = 0x0014   // RC4 > SCK1 (bi-directional)        
        End Sub

    'This is a PPS chip, so, needs to make the PPS match these assignments
    #DEFINE SPI_DI     portC.6    //SDIx  SO/Pin2
    #DEFINE SPI_DO     portC.5    //SDOx  SI/Pin5
    #DEFINE SPI_SCK    portC.4    //SCKx  SCK/Pin6
    #DEFINE SPI_CS     portC.3    //      CS/Pin1


#DEFINE HWSPIMode   MasterFast
#DEFINE HWSPIClockMode  SPI_SS_0 + SPI_CPOL_0 + SPI_CPHA_0
SPIMode (HWSPIMode,  HWSPIClockMode )


Dim Mydata as Byte = 0

//WRITING AND READING BYTES (23LCV1024 1Mbit RAM CHIP) with DIRECT COMMANDS via the HWSPIport: 

//WRITE BYTE:
SPI_CS=0
FastHWSPITransfer 0x2   // WRITE instruction
FastHWSPITransfer 0x0   // MSB 24bit address 0x000008
FastHWSPITransfer 0x0   // ||
FastHWSPITransfer 0x8   // LSB
FastHWSPITransfer 0xAF  //Write data 0xAF=175
SPI_CS=1                //Write sequence is terminated

//READ BYTE:
SPI_CS=0
FastHWSPITransfer 0x3   //READ instruction
FastHWSPITransfer 0x0   // MSB 24bit address 0x000008
FastHWSPITransfer 0x0   // ||
FastHWSPITransfer 0x8   // LSB 
SPITransfer 0x0, Mydata //Dummy address for data to be shifted out
SPI_CS=1                //Read sequence is terminated

GLCDPrint (0, 20, Mydata)

[Roger Jönsson]

Changes to make sequential write and read:

DIM Readbyte as byte=0

//SEQUENTIAL WRITING AND READING: (23LCV1024 1Mbit RAM CHIP)

//WRITE BYTES
SPI_CS=0
FastHWSPITransfer 0x2   // WRITE instruction
FastHWSPITransfer 0x0   // MSB 24bit START ADDRESS
FastHWSPITransfer 0x10   // ||
FastHWSPITransfer 0x64  // LSB
//Write bytes sequentially:
FastHWSPITransfer 10    //Write data
FastHWSPITransfer 15    
FastHWSPITransfer 20    
FastHWSPITransfer 25    
FastHWSPITransfer 35    
SPI_CS=1                //Write sequence is terminated

//READ BYTES:
SPI_CS=0
FastHWSPITransfer 0x3   // READ instruction
FastHWSPITransfer 0x0   // MSB START ADDRESS
FastHWSPITransfer 0x10   // ||
FastHWSPITransfer 0x64  // LSB
//Read bytes sequentially:
SPITransfer 0x0, ReadByte //Dummy address for data to be shifted out
    GLCDPrint (0, 30, ReadByte)
SPITransfer 0x0, ReadByte 
    GLCDPrint (20, 30, ReadByte)
SPITransfer 0x0, ReadByte 
    GLCDPrint (40, 30, ReadByte)
SPITransfer 0x0, ReadByte 
    GLCDPrint (60, 30, ReadByte)
SPITransfer 0x0, ReadByte 
    GLCDPrint (80, 30, ReadByte)
SPI_CS=1                //Read sequence is terminated