; Katie Keim and Chase Kragenbrink CSC 225-05
;trap.asm

.ORIG x3300

ST R0, SaveR0  ;
ST R1, SaveR1  ;
ST R2, SaveR2  ;
ST R3, SaveR3  ;

LD R2, ENTER;   Load <enter> into R2
NOT R2, R2   ;    
LD R3, SaveR0;

READY LDI R1, KBSR;  Keyboard status
      BRzp READY;    if not ready, return

      LDI R0, KBDR;  LINE 10
      ADD R1, R0, R2;
      NOT R1, R1;
      BRz FINISH;
      STR R0, R3, #0;
      ADD R3, R3, #1;

DISPLOOP LDI R1, DSR;
         BRzp DISPLOOP;        if not ready go back

      STI R0, DDR;   
      BRnzp READY;

FINISH AND R0, R0, #0; Finish and return
       ADD R3, R3, #1;
       STR R0, R3, #0;

       LD R0, SaveR0; Restore registers
       LD R1, SaveR1;
       LD R2, SaveR2;
       LD R3, SaveR3;

      RET;

KBSR .FILL xFE00
KBDR .FILL xFE02
DSR  .FILL xFE04
DDR  .FILL xFE06
ENTER .Fill x000A

SaveR0 .FILL x0
SaveR1 .FILL x0
SaveR2 .FILL x0
SaveR3 .FILL x0

.END