prog29.asm

主要是8051源代码

;  PROG29 - Working through the Emulator  
;
;  Start with the Serial Interface.    
;
;  This Application waits for 2 Seconds and then Sends "A" by "Bit Banging" to
;   the Console.  Note that Variables at at Address 080h and Greater.
;
;  Myke Predko
;  98.06.25
;
;  Hardware Notes:
;  DS87C520 is used as the Microcontroller
;   - Oscillator Speed is 20 MHz
;  P2.7 is Console Serial Output

;  Constant Declarations
define SerOut=P2.7              ;  Serial Output Bit

;  Variable Declarations


;  Macros


;  Mainline
 org 0                          ;  Execution Starts Here
MainLine:                       ;  Mainline of the Program

  mov     R2,#54                ;  Delay for 2 Seconds
  mov     R1,#0
  mov     R0,#0
LongDlay:                       
  djnz    R0,LongDlay
  djnz    R1,LongDlay
  djnz    R2,LongDlay

  mov     A,#'A'                ;  Send the "A" Character
  acall   SendChar

  ajmp    Mainline              ;  


;  Subroutines
SendChar:                       ;  Send the Serial Character
  mov	 R0,#10		;  We're Actually Sending 10 Bits

  clr	 C	       	;  First Bit is a "0"

SCLoop:			;  Loop Here for Each Bit

  mov	 SerOut,C       ;  Output the Bit in the Carry Flag

  mov	 R1,#170	;  Delay to 104 usecs (520 Cycles) per loop
SCLoop1:
  djnz	 R1,SCLoop1
  nop

  setb	 C		;  Shift the Next Bit to Carry
  rrc 	 A		;   And Load in a "1" for Stop Bit

  djnz	 R0,SCLoop

  ret