topic Re: Displaying ADC readout through SCI in 8-bit Microcontrollers

Displaying ADC readout through SCI

berb_15 — Thu, 29 Oct 2020 09:20:36 GMT

Hello all. I'm trying to read an analog input ranging from 0 to 2.5 volts, convert it to a digital signal, and read the bits outputted through hyperterminal (for now...). I will eventually be using a gui to take these bits and make sense of them but just want to get a solid reading first. I am getting a reading but it is a bunch of letters and symbols on hyperterminal and I'm not sure why. When I remove my input I get a bunch of "]"'s, so I know it's reading something from the ADC when it's hooked up. Below is my code and a picture of my output. Any ideas would be appreciated. Please let me know if anything should be changed or is unessesary as I'm new to microcontrollers, Thanks!

My hardware/Software:

* DEMOQE128 board

* MC9S08QE128

* Code Warrior

My code:

int PyrRding;

void main(void) {

 
/*******Set up SCI Registers********/
SCI1C1=0x40;
SCI1C2=0x08;
/***********************************/


PTCDD_PTCDD5=1;
PTCD_PTCD5=1;
SCI1BDL=0x1A;//baud rate=9600bps and bus freq=4MHz.


 /**********Pyranometer ADC**********/
ADCSC1_ADCO = 1;        // enable continuous conversion
ADCCFG_MODE = 0x00;     // 8 bit mode
PTADD = 0x00;           // initialize as input
/************************************/


/****************First ADC to SCI*************/
for(;;){

ADCSC1_ADCH = 0x00;           // set channel PTA0
ADCSC1 = 0;                   // Commence new conversion Ch0

while (ADCSC1_COCO == 0){}    // Wait until conversion complete
PyrRding = ADCRL;             // output 8bit ADC to PyrRding variable

   
while (SCI1S1_TDRE == 0){};   // Wait for the transmitter to be empty
SCI1D = PyrRding;             // Stores new data to be transmitted via serial port
SCI1S1_TDRE = 0;              // Clear flag to send

__RESET_WATCHDOG();

 }
/**********************************************/

}

My output:

Re: Displaying ADC readout through SCI

PeterHouse — Tue, 14 Apr 2009 08:28:39 GMT

You are sending a raw byte value to a device which is expecting an ASCII value.

The byte valuereturned from the ADC varies between 0 and 255 decimal or 0 to FF in Hexadecimal. To display the numeral "0" to "9" on hyperterminal you must send the hexadecimal values 30 to 39.

There are lots of ASCII tables on the internet if just google the acronym ASCII or just go to www.asciitable.com

You will probably need to write a conversion routine or use one of the stream formating functions like sprintf to format your data before sending it to the serial port to Hyperterminal.

Good Luck,

Peter House

Re: Displaying ADC readout through SCI

berb_15 — Tue, 14 Apr 2009 08:50:25 GMT

Thanks Peter House that makes perfect sense. I'm going to do a little research on converting the data and the sprintf function but if you have any aditional suggestions or examples I'm all ears!! Thanks again.

Re: Displaying ADC readout through SCI

bigmac — Tue, 14 Apr 2009 11:15:04 GMT

Hello,

The use of sprintf() to do what you require is somewhat over-kill. Here is a much more compact function to do the binary to ASCII conversion. It uses inline assembly code for fast operation. The numeric ASCII characters are written to the buffer, and null termination also occurs.

void conv_ASCII( byte val, byte *buf)
{
   __asm {
      LDA   val
      CLRH
      LDX   #10      // Divisor
      DIV
      PSHH           // LS digit
      CLRH
      DIV
      PSHH           // 2nd digit
      LDHX buf
      ADD   #'0'     // Convert to ASCII digit
      STA   ,X       // MS digit
      PULA
      ADD   #'0'     // Convert to ASCII digit
      STA   1,X
      PULA
      ADD   #'0'     // Convert to ASCII digit
      STA   2,X      // LS digit
      CLR   3,X      // Null termination
   }
}

The function might be used in the following manner -

byte buffer[4];

...

ADCSC1 = 0; // Commence new conversion Ch0
while (ADCSC1_COCO == 0){} // Wait until conversion complete
conv_ASCII( ADCRL, buffer);

while (*buffer) { // Check for null character

while (SCI1S1_TDRE == 0){}; // Wait for transmit buffer empty
SCID = *buffer++; // Write character to SCI

}

while (SCI1S1_TDRE == 0){}; // Wait for transmit buffer empty
SCID = ' '; // Separator space

Regards,

Mac

Re: Displaying ADC readout through SCI

berb_15 — Wed, 15 Apr 2009 00:18:32 GMT

Thanks Mac, I've heard the sprintf() function uses a lot of memory and like you said my program isn't that intricate... It looks like the code you posted is exactly what I need. I'm assuming I can run that assembly code right in with my standard c++ code? I'm going to try to implement this after my classses today and let you know how it goes! Thanks again.

Re: Displaying ADC readout through SCI

RichTestardi — Wed, 15 Apr 2009 04:16:05 GMT

Hi,

Here's a simple idea if you are looking for alternatives...

> I'm trying to read an analog input ranging from 0 to 2.5 volts,

> convert it to a digital signal, and read the bits outputted through

> hyperterminal (for now...).

You can just load StickOS onto the QE and then log into it with Hyper Terminal (9600/8/n) and write a program like:

10 dim a as pin pta0 for analog input
20 while 1 do
30 print a
40 sleep 500 ms
50 endwhile

And then save and run it, and the number of millivolts on pin pta0 will be printed to the Hyper Terminal twice a second. You can then set the program to autorun and it will do that whenever the MCU is powered up.

When I run it, I see my pot (on the DEMOQE board), like:

> run
2133
2132
2135
2133

<Ctrl-C>
STOP at line 40!
>

Press <Ctrl-C> to stop the program (to edit it, debug it, etc.).

If you want downloads of StickOS, for the 51QE128 or 9S08QE128, they are at:

http://www.cpustick.com/downloads.htm

You can find full documentation there, as well.

-- Rich

Re: Displaying ADC readout through SCI

berb_15 — Wed, 15 Apr 2009 06:53:59 GMT

Thanks Rich I actually just learned about StickOS today. I think I'm going to skip for this project but I'm definitely going to look into using StickOS in the future and see what it's all about...

Re: Displaying ADC readout through SCI

bigmac — Wed, 15 Apr 2009 10:26:22 GMT

Hello,

berb_15 wrote:
... I'm assuming I can run that assembly code right in with my standard c++ code?

The code is actually a C function - for the moment I suggest that you stick with C code, rather than C++, for your program.

Regards,

Mac

Re: Displaying ADC readout through SCI

berb_15 — Fri, 17 Apr 2009 00:20:25 GMT

Mac, I tried to implement your code but I'm throwing an error. I think it's probably something small or dumb but unfortunately I'm not fluent in coding...

SCID = *buffer++; // Write character to SCI

At this line it says: Wrong type or not an lvalue

I used byte buffer[4]; at the beginning of my code to declare it but somethings still not right... Should the array be a different size??

Thanks in advance.

Re: Displaying ADC readout through SCI

RichTestardi — Fri, 17 Apr 2009 00:28:14 GMT

You might try "SCI1D", assuming you are using UART 1.

Or did you forget the ";" on the preceding line, or forget to include "MC9S08QE128.h"?

If you get really stuck, you can usually right-click on a .c file and select "Preprocess" to see exactly what the compiler is complaining about.

-- Rich

Re: Displaying ADC readout through SCI

berb_15 — Fri, 17 Apr 2009 00:36:05 GMT

I'm sorry I did actually use SCI1D I just copied Macs code above for my post. I'll play around with it and see if I can come up with anything.

Re: Displaying ADC readout through SCI

RichTestardi — Fri, 17 Apr 2009 00:46:56 GMT

Oh, and *I'm* sorry -- I read your code too fast...

You can't do a "++" on a variable declared like:

byte buffer[4];

Change that to a "byte *buffer;" and make sure it points to allocated memory.

Re: Displaying ADC readout through SCI

bigmac — Fri, 17 Apr 2009 02:51:24 GMT

Hello,

Sorry about the misleading information. Rich T is absolutely correct on both counts. The following revised code should compile.

byte buffer[4], *p;

...

ADCSC1 = 0; // Commence new conversion Ch0
while (ADCSC1_COCO == 0){} // Wait until conversion complete
conv_ASCII( ADCRL, buffer);

p = buffer;

while (*p) { // Check for null character

while (SCI1S1_TDRE == 0){}; // Wait for transmit buffer empty
SCI1D = *p++; // Write character to SCI

}

while (SCI1S1_TDRE == 0){}; // Wait for transmit buffer empty
SCI1D = ' '; // Separator space

Regards,

Mac

Re: Displaying ADC readout through SCI

berb_15 — Tue, 21 Apr 2009 07:00:13 GMT

Ahh ok that works for me now. Thanks a lot for the help!!

Re: Displaying ADC readout through SCI

pinkiler — Thu, 05 Jan 2012 02:24:19 GMT

berb_15 or you can send me your working code of the program. On my mailtomazvalic20@gmail.com).

Thanke you very much!