Need some help with SXB PWM code.. (Getting error _TrisC)

Kd7lax · 2007-09-08 08:15

Hi guys,
Just got my SX Blitz key today and my SX48 Proto Board, and I have been running through the new draft of the Practical SXB book.
On the experiment that talks about PWM (page 83) they give me a piece of code to try and it keeps giving me an error every time I try and use it.
Here is the code ( I moded it to work with my 48chip )

DEVICE sx48, OSC4mhz
FREQ 4_000_000

Led    PIN    RC.0

duty    VAR    Byte

PROGRAM Start

Start:
    DO
        FOR duty = 0 TO 254
             PWM Led, duty, 2
        NEXT
        FOR duty = 255 TO 1 STEP -1
             PWM Led, duty, 2 
        NEXT
        PAUSE 50
    Loop

The error I get is " line 93, error 3, pass 2: Symbol <_TrisC> is not defined" And the same error appears on line 127.
This error is in the assembled code
Here is the assembled code:

  SETB IND.0                    
  MOV W,#$1F                    
  MOV M,W                       
  MOV !RC,IND                   
  MOV FSR,#$10                  

  CJAE duty,#254,@__NEXT_duty_1  ;        NEXT
  INC duty                      
  JNZ @__FOR_duty_1             
__NEXT_duty_1:                  

  MOV duty,#255                  ;        FOR duty = 255 TO 1 STEP -1
__FOR_duty_2:                   

  MOV FSR,#__TRIS                ;             PWM Led, duty, 2 
  MOV W,#$0F                    
  MOV M,W                       
  MOV !RC,W                     
  MOV IND,W                     
  MOV W,#$1F                    
  MOV M,W                       
  CLRB IND.0                    
  MOV !RC,IND                   
  MOV FSR,#$10                  
  MOV __PARAM1,#2               
  CLR __PARAM2                  
  MOV __PARAM3,#2               
  MOV __PARAM4,#108             
  ADD __PARAM2,duty             
  MOVB Led,C                    
  DJNZ __PARAM4,@$-6            
  DJNZ __PARAM3,@$-9            
  DJNZ __PARAM1,@$-16           
  [color=#009900]MOV FSR,#__TRISC   // It Highlighted this when I ran the debugger     [/color]     
  SETB IND.0                    
  MOV W,#$1F                    
  MOV M,W                       
  MOV !RC,IND                   
  MOV FSR,#$10                  

  CJBE duty,#1,@__NEXT_duty_2    ;        NEXT
  SUB duty,#1                   
  JC @__FOR_duty_2              
__NEXT_duty_2:                  

  MOV __PARAM2,#50               ;        PAUSE 50
  MOV __PARAM3,#4               
  MOV __PARAM4,#28              
  DJNZ __PARAM4,@$              
  DJNZ __PARAM3,@$-3            
  DJNZ __PARAM2,@$-10           

  JMP @__DO_1                    ;    Loop
__LOOP_1:

Whats going on here? I have checked over my code several times and tried several different things...

It might just be that I am trying to do this at 1:21 AM :P and it's entirely possible that in the morning it will be obvious to me... but I thought I would check here first..

Thanks guys
-Mike

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Visit my website @ www.kd7lax.com- Devoted to ham radio

Post Edited (Kd7lax) : 9/8/2007 8:24:58 AM GMT

Bean · 2007-09-08 11:38

Mike,
This is a known issue when using PWM on the SX48.
See this thread for the work-around http://forums.parallax.com/showthread.php?p=597707

This should work:

 
DEVICE sx48, OSC4mhz
FREQ 4_000_000

Led    PIN    RC.0

 
__TRISA CON __TRIS
__TRISB CON __TRIS
__TRISC CON __TRIS
__TRISD CON __TRIS
__TRISE CON __TRIS



duty    VAR    Byte

PROGRAM Start

Start:
    DO
        FOR duty = 0 TO 254
             PWM Led, duty, 2
        NEXT
        FOR duty = 255 TO 1 STEP -1
             PWM Led, duty, 2 
        NEXT
        PAUSE 50
    Loop

Bean.

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The first rule to being successful is "Learn from your mistakes",
The second rule is "Be willing to make mistakes"
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·

Kd7lax · 2007-09-08 21:22

Thanks for your help!

-Mike

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Visit my website @ www.kd7lax.com- Devoted to ham radio

T&E Engineer · 2007-09-09 10:36

I have read a little about PWM but don't understand it's purpose with application to LEDs. Is it used to simply "fade" LEDs? I have seen an approach that uses STB lines for PWM control on some Micrel MIC5821's or pin-for-pin compatible Allegro A6821's. See attached. Can someone shed some light to this PWM and why it seems to be such a hot topic?

I am going with this approach using some Allegro A6821 (which are simply serial versions of UDN2803's). Their cascadable 3-pin interface (Data, Clock, and Strobe) should work like 74HC595's so It should not be too difficult. However I may use some N-Channel FETS between the cathodes and the A6821's to allow for more current in scrolling in all directions (not just left and right).

How does this hardware STroBing (PWM) compare with PWM control in software for the SX-28 or 48, etc..?

Post Edited (T&E Engineer) : 9/9/2007 10:41:30 AM GMT

Bean · 2007-09-09 13:06

Yeah, it is a way to vary the intensity by controlling the ratio of "on" time and "off" time.
There are various methods. PWM, PFM, etc.

The analog way to control intensity would be to generate an analog voltage, and use that voltage to control the current to the device. But PWM does it in a purly digital way.

Bean.

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The first rule to being successful is "Learn from your mistakes",
The second rule is "Be willing to make mistakes"
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
www.hittconsulting.com
·

Need some help with SXB PWM code.. (Getting error _TrisC)

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