AnsweredAssumed Answered

S12X SPI - reading concern

Question asked by Pratima Vishwakarma on Feb 11, 2019
Latest reply on Feb 13, 2019 by Pratima Vishwakarma

Hello Sir,

This is regarding the SPI communication with RF transceiver. I am trying to establish Master- Slave communication using SPI with microcontroller (Master) and RF transceiver (Slave). The microcontroller used is S12X series : MC9S12XEQ512 (SPI1 port is used), RF transceiver which has 3 wire interface for SPI communication (SCLK, DIO, CS).

The microcontroller pins MISO1 and MOSI1 are shorted together on board to interface with DIO line of 3 wire- SPI Transceiver IC.


Here is the following code:

#define W_OSC 0x45;    //write command: 0x1 and register address as 0x05: transceiver//

#define W_PC 0x40;

#define RD_OSC 0x85;   //read command: 0x2 and register address as 0x05: transceiver//


void SPI_TXR_Init(void)


unsigned char Test0;

unsigned char STATUS1;

unsigned char STATUS2;




   SPI1DR=0x00FF;                //start of sending SCK //





   SPI1DRH=W_OSC;               //for writing//  

   SPI1DRL=0xB0;                    // 0000 1100 oscillator frequency which is 176//

   delay(50);                              //defined//       



   SPI1DRH=RD_OSC;             // for reading//



   PTP_PTP3=1;                        // CS high//


   PTP_PTP3=0;                        // CS low//


   DDRP_DDRP0=0;                   //Micro SPI pins, MISO_R for input//

   DDRP_DDRP1=0;                  // Micro SPI pins MOSI_R for input//

   PTP_PTP1=0;                         // Micro SPI pins MOSI_R is low/

   PTP_PTP0=0;                         // Micro SPI pins MISO_R is low/




   STATUS1=SPI1DRH;             //tried to store data here//






   SPI1DRH=W_PC;                   //for writing//

   SPI1DRL=0x30;                      // 0011 0000 Enable Mixer, Baseband enable , disable PA only//


   Test0=SPI1SR;                       //want to read this as well//




void main(void)


//code for clock setting to 25MHz//

//port setting//

DDRP_DDRP0=0;                 //MISO_R for input//

DDRP_DDRP1=1;                //MOSI_R for output//

DDRP_DDRP2=1;                 //SCK_R for output//

DDRP_DDRP3=1;                //CS_R is output//


PTP_PTP3=1;                          // CS_R is high/

PTP_PTP1=0;                        // MOSI_R is low/

PTP_PTP0=0;                        // MOSI_R is low/

PTP_PTP2=1;                        // SCK is set high//

//SPI initialization//

SPI1CR1_SPE=1;                   //SPI enabled, port pins are dedicated to SPI functions.//

SPI1CR1_SPIE=0;                 // SPI interrupts disabled.//

SPI1CR1_SPTIE=0;              // interrupt request are disabled//

SPI1CR1_MSTR=1;              //SPI is in master mode.//

SPI1CR1_CPOL=0;               //Active-high clocks selected. In idle state SCK is low.//

SPI1CR1_CPHA=0;              //Sampling of data occurs at odd edges//

SPI1CR1_SSOE=0;               //SS is not enabled//

SPI1CR1_LSBFE=0;              //MSB first//

SPI1CR2=0x49;                     // 0100 1001 (16 bit transfer, MODFEN=0, BIDIROE=1, SPC0=1, SS pin used, ouput buffer disabled,master mode //

SPI1BR=0x07;                           // Baud rate: 97.66 kbit/s in D-10B (25MHz / 256)//

SPI1CR1_SSOE=1;                   //SS is enabled//


//Powering up of TXR//

PORTA_PA0=1;                                  // Drive high for normal operation of MAX7032//


PTP_PTP3=0;                                    // CS_R is low to enable the slave/


PORTA_PA1=1;                                 // Drive high for normal operation of MAX7032, TX/-RX_R//





For this code, I am able to send commands to RF transceiver from microcontroller, but when it comes to reading, I didn’t get any data.

I tried reading for address register: 0x05 and 0x00, but the code does not return any value.

Could you please check and let me know where is the problem?

Also, would like to know what is the procedure of reading the data from SPI so as to ensure the data is written to slave is correct.