;Toggling PE3 to activate the optoisolator for Dragon12 Plus Trainer Board 
;PE3 of PORTE actiavtes the Base of Optoisolator (CNY75GB) on Dragon12+ board
;This program toggles PE3 to turn on and off the optoisolator. 
;The collector (COL) and emittter (EMT) pins of the Optoisolator are available to user (see bottom of the Dragon12 board).
;For Optoisolator See Chapter 15 of HCS12 book by Mazidi & Causey
;The Optoisolator used in the Dragon12 is CNY75GB. Google it to get the data sheet

;Connect +5V pin on Dragon12 to positive side of an LED (long leg)
;Connect the negative side of the LED (short leg) to COL pin of Opto on Dragon12+ board
;Connect the EMT pin of Opto (on Dragon12) to GND pin. Now, by running this program the lED goes on and off.
;If you use this optoisolator to control an external device such as horn and lamp use external power as shown in chapter 15.  
       
#include "C:\Reg9s12.H"
   
 
;----------------------USE $1000-$2FFF for Scratch Pad and Stack 
R1      EQU     $1001
R2      EQU     $1002
R3      EQU     $1003

;code section
        ORG   $2000     
      	LDS   #$2000    ;Stack
        BSET  DDRE,%00001000     ;PE3 as Output pin for optoisolator
   
;-------Turn on and off the optoisolator at PE3

BACK    BSET PORTE,%00001000     ;PE3=1 to turn on optoisolator
    	JSR DELAY        
    	BCLR PORTE,%00001000     ;PE3=0 to turn off optoisolator
    	JSR DELAY        
      	  
	BRA BACK              ;Keep doing it    
  
;----------DELAY
DELAY

        PSHA		;Save Reg A on Stack
        LDAA    #100	;100 msec delay  
        STAA    R3		  
;--1 msec delay. The D-Bug12 works at speed of 48MHz with XTAL=8MHz on Dragon12+ board
;Freq. for Instruction Clock Cycle is 24MHz (1/2 of 48Mhz). 
;(1/24MHz) x 10 Clk x240x10=1 msec. Overheads are excluded in this calculation.         
L3      LDAA    #10
        STAA    R2
L2      LDAA    #240
        STAA    R1
L1      NOP         ;1 Intruction Clk Cycle
        NOP         ;1
        NOP         ;1
        DEC     R1  ;4
        BNE     L1  ;3
        DEC     R2  ;Total Instr.Clk=10
        BNE     L2
        DEC     R3
        BNE     L3
;--------------        
        PULA			;Restore Reg A
        RTS
;-------------------