main.cpp

00001 
00002 // program used to read SPI 12 bit Encoder AMT203-V in steps of 16
00003 #include "mbed.h"
00004 
00005 Serial pc(USBTX, USBRX); // tx, rx
00006 SPI EncoderSpi(p5, p6, p7);//Mosi Miso Sclk
00007 DigitalOut cs(p8); //Chip select
00008 
00009 uint16_t EncoderByteData = 0;
00010 uint16_t Encoderposition_last = 0;
00011 uint8_t temp[2];
00012 uint16_t Steps;
00013 void wait_ms(int us);
00014 
00015 
00016 uint8_t SPI_T (uint8_t SPITransmit)//Repetive SPI transmit sequence
00017 {
00018     uint8_t SPI_temp = 0;  //vairable to hold recieved data
00019     cs=0;     //select spi device
00020     SPI_temp = EncoderSpi.write(SPITransmit);//send and recieve
00021     cs=1;//deselect spi device
00022     return(SPI_temp);      //return recieved byte
00023 }
00024 
00025 void start()
00026 {
00027     uint8_t recieved = 0xA5;//just a temp vairable
00028     EncoderByteData  = 0;//reset position vairable 
00029     cs=0;  
00030     SPI_T(0x10);//issue read command     
00031     wait_ms(50);//give time to read. Timmig is critical
00032     
00033     while (recieved != 0x10) //loop while encoder is not ready to send
00034     { 
00035      recieved = SPI_T(0x00); //cleck again if encoder is still working
00036      wait_ms(1); //again,give time to read. Timmig is critical
00037     }
00038 
00039      temp[0] = SPI_T(0x00); //Recieve MSB
00040      temp[1] = SPI_T(0x00); // recieve LSB      
00041      cs=1;
00042         
00043      temp[0] &=~ 0xF0;//mask out the first 4 bits
00044      EncoderByteData  = temp[0] << 8; //shift MSB to correct EncoderByteData in EncoderByteData message
00045      EncoderByteData  += temp[1]; // add LSB to EncoderByteData message to complete message            
00046      wait_ms(1);//again,give time to read. Timmig is critical
00047 }
00048 
00049 int main()
00050 {  
00051     EncoderSpi.format(8,0);
00052     EncoderSpi.frequency(8000000);
00053     
00054  while(true)
00055     {
00056    
00057      if (EncoderByteData != Encoderposition_last) //if nothing has changed dont wast time sending position
00058     {
00059       Encoderposition_last = EncoderByteData ; //set last position to current position         
00060     }
00061      else
00062     {   
00063       start(); //if something has changed in position, catch it
00064     } 
00065         Steps = EncoderByteData;        
00066        //pc.printf("Data = %d \n", EncoderByteData ); //actual byte reading
00067         pc.printf("Data = %03d \n", Steps/16 );
00068     }
00069     
00070 }