servcent.asm

主要是8051源代码

;  ServCent -  Centre an R/C Servo 
;
;  This is the first program for the Model Airplane Application
;   Demonstration.  This Program outputs a 1.5 msec Pulse once every
;   20 msecs to Centre the Servo.  The Interrupt Routine outputs a signal
;   For two Servos.  
;
;  Each Timer Interrupt Loop Takes 18 usecs.  Therefore, at the 1 msec 
;   Extreme, a value of 56 is used.  For the Other Extreme, 2 msec, a value
;   of 111 is used.  For the Middle Position, a value of 83 is used.
;
;  Myke Predko
;  98.05.03
;
;  Hardware Notes:
;  89C2051 Running at 10 MHz
;  The 80C520's Timer 0 Running in Mode 0
;  P1.6 is Connected to a Radio Control Servo (Servo 1)
;  P1.7 is Connected to a Radio Control Servo (Servo 2)

;  Variable Declarations
Servo0 EQU 010h                 ;  Position of the Aileron Servo (at P1.6)
Servo1 EQU 011h                 ;  Position of the Elevator Servo (at P1.7)  

 org 0
  ajmp   Mainline

 org 0Bh                        ;  Timer0 (Real Time) Interrupt

  mov   TH0,#191                ;  Reload the Timer Interrupt
  mov   TL0,#00                 ;  To Interrupt Again in 20 msecs

  push  ACC                     ;  Save the Accumulator
  push  PSW                     ;  Save the Status Register

  mov   A,#0C0h                 ;  Turn ON the Servo's Pulses
  orl   A,P1
  mov   P1,A

  mov   B,#0                    ;  Use "B" as the Loop Counter

IntLoop:                        ;  Loop Around Until Both Servos Counts are met

  mov   A,B                     ;  Get the Current Count Value
  clr   C
  subb  A,Servo0                ;  Is Count Past the Current Position?
  mov   P1.6,C                  ;  Save the Carry as the Aileron Output

  mov   A,B
  clr   C
  subb  A,Servo1
  mov   P1.7,C                  ;  Save the Carry as the Elevator Output

  inc   B                       ;  Increment the Counter

  orl   C,P1.6                  ;  Are Both Control Bits Low?

  jc    IntLoop                 ;  Loop Back, If Either Bit Set

  pop    PSW                    ;  Restore the Registers Pushed onto the Stack
  pop    ACC

  reti


Mainline:                       ;  Program Mainline

  mov    P1,#03Fh               ;  Turn Off the Pulses to the Elevators and Ailerons

  mov    TMOD,#%00000001        ;  Timer0 - Uses Internal Clock
                                ;         - Run in Mode 1
  mov    TCON,#%00010000        ;  Start Timer0 running

  mov    TH0,#191               ;  Setup the 20 msec Delay to the Timer Interrupt
  mov    TL0,#00

  mov    Servo0,#83             ;  Setup the Servos to 1.5 msec Delays
  mov    Servo1,#83

  mov    IE,#%10000010          ;  Enable the Timer 0 Interrupt

;  Now, Do the Looping Output

MainLoop:                       ;  Come Back Here After Decrementing P3

  ajmp   MainLoop               ;  Just Loop Around Forever