topic Re: 9S08QG8 - Combination problem ADC PWM in 8-bit Microcontrollers

9S08QG8 - Combination problem ADC PWM

ernestsnaith — Tue, 27 Feb 2007 01:01:24 GMT

I am having some problems with MC9S08QG8. I have two of these microcontrollers, one takes an analogue signal converts it to 8 bit and sends via serial. The other receives this message and turns it in two a PWM signal.

This is part of a optical communications project and I therefore have some circuitry between the Tx and Rx pins of the MC’s but I have removed this at the moment. I therefore have the Tx pin on one MC connected directly to the Rx on the other.

The system behaves roughly as I would have expected however at certain voltage inputs the PWM jumps to a different pulse width. This happens a lot and I cant see a pattern, although an increasing PW can be seen as the voltage increases.

To find cause of problem I have tried various parts on there own and all were successful, including ADC to Serial, ADC to PWM. I also wrote code that incremented an integer which was sent via serial and converted to PWM. Therefore i have no idea what the problem is.

All I can think of is lack of any additional components to get rid of noise. Please could someone advise me to how the input/outputs should be connected and any other things I should be aware of.

Thanks

Code:

// *************************************// **                                 **// ** Name: ADC to SCI Transmit       **// ** Verion: 1.0                     **// ** Desc: PA1 as ADC sent with SCI  **// ** MC: 9S08QG8                     **// **                                 **// *************************************#include <hidef.h> /* for EnableInterrupts macro */#include "derivative.h" /* include peripheral declarations */int Temp;void main(void) {  int i;                      // For Loop Var  int j;                      // For Loop Var  ADCSC1 = 0x00;              // Set to Channel 1  ADCSC2 = 0x00;              // Settings  ADCCFG = 0x90;              // Speeds  APCTL1 = 0x01;              // Configure Pin as ADC       SCIBDL = 0xFF;              // Select baud rate   SCIC1 = 0x12;               // Settings   SCIC1_PT = 0;  SCIC2_TE = 1;               // Enable Transmitter                              EnableInterrupts;    for(;;)                     // Loop Forever  {          for(i=1;i<50;i++)         // PAUSE    {      for(j=1;j<254;j++)      {      }          }      ADCSC1 = 0x00;            // Write for conversion to take place    while (ADCSC1_COCO == 0){}// Wait until conversion complete    Temp = ADCRL;      SCID = Temp;              // ADC value sent    SCIS1_TDRE = 0;           // Clear flag to send            __RESET_WATCHDOG();   }}

Code:

// *************************************// **                                 **// ** Name: SCI Recieve to PWM        **// ** Verion: 1.0                     **// ** Desc:                           **// ** MC: 9S08QG8                     **// **                                 **// *************************************#include <hidef.h> /* for EnableInterrupts macro */#include "derivative.h" /* include peripheral declarations */int Data;int BadData;void main(void) {  // VARIABLES  int i;                      // For Loop Var  int j;                      // For Loop Var  int Temp=0;    // PWM   TPMSC = 0x0F;     // Settings  TPMMODH = 0x00;   // Period H  TPMMODL = 0xFF;   // Period L  TPMC0SC = 0x28;   // Settings  TPMC0VH = 0x00;   // Duty H  TPMC0VL = 0xAF;   // Duty L    // OUTPUT  PTADD_PTADD0 = 1;           // Set PTB7 as an output    // SCI  SCIBDL = 0x7F;              // Select baud rate   SCIC1 = 0x12;               // Settings 9 bit with parity   SCIC2_RE = 1;               // Enable Transmitter  SCIC2_TE = 0;  EnableInterrupts;    for(;;)                     // Loop Forever  {          for(i=1;i<10;i++)          // PAUSE    {      for(j=1;j<254;j++)      {      }    }    if(SCIS1_RDRF == 1)     {      if((SCIS1_NF == 0) && (SCIS1_PF == 0))      {        Data = SCID;        TPMC0VH = 0x00;   // Duty H          TPMC0VL = Data;   // Duty L             }      else      {        BadData = SCID;      }    }    __RESET_WATCHDOG();       // feeds the dog  }}

Alban clarified subject

Message Edited by Alban on 2007-02-26 05:50 PM

Re: 9S08QG8 - Combination problem ADC PWM

joerg — Tue, 27 Feb 2007 01:48:52 GMT

Dear ernestsnaith
After a fast look at your code, it think you have a timing problem! Since there is no synchronization between sender and receiver, the last should be programmed to do the receiving with a interrupt routine. The interrupt routine should the set a flag to the main loop so you can then update the PWM output. For the sending routine i would also wait in a loop until the SCI has sent the data. This way you are sure not overrunning the UART with new data.

Saluti Joerg

Alban clarified subject

Message Edited by Alban on 2007-02-26 05:51 PM

Re: 9S08QG8 - Combination problem ADC PWM

bigmac — Tue, 27 Feb 2007 02:27:06 GMT

Hello,

On this occasion I will have to disagree with Joerg.

Since each ADC sample is suitably delayed, polling for the received character should work. However, the polling loop to wait for RDRF to be set should be tight - the delay loops in the code are unnecessary, and may result in SCI receive overflow.

In addition, since 9-bit mode is used, my understanding is that the R9 bit must be read, in addition to SCID, so that the RDRF flag will be cleared.

In the SCI transmit code, there seems to be a misunderstanding of the operation of the TDRE flag (but probably won't affect the current operation). The state of the TDRE flag should be tested, and when it becomes set, only then should the byte be sent. The flag will automatically clear, and then become set again when a further byte can be sent.

Regards,

Mac

Re: 9S08QG8 - Combination problem ADC PWM

ernestsnaith — Tue, 27 Feb 2007 06:15:39 GMT

Made all changes and worked first time, thanks all.