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Example Disassembly from Mac Plus
Trap Dispatcher Code (from vector at $0028)
This is the code that is called whenever a toolbox or operating system trap is executed it determines the address of the trap and transfers control to it. 
Note that this was performed with a beta version of DASM and so the disassembly here may differ slightly in appearance from other disassemblies you produce.

Note too that all  values are Hexadecimal. 

401F52  SUBQ.L  #0002,A7                    ;We enter with A7 pointing to PC
401F54  MOVEM.L  D1/D2/A2,-(A7)       ;We've effectively pushed 14 bytes
401F58  MOVE.L  10(A7),A2                    ;A2 points to the trap word
401F5C  MOVE.W  (A2)+,D2                      ;Now D2 holds the trap word.
401F5E  MOVE.L  A2,10(A7)                     ;The stack now holds the address after the 
                                                                ;trapword -- We'll return there.
401F62  MOVE.W  D2,D1                           ;Now D1 and D2 both hold the trapword.
401F64  ANDI.W  #1FF,D2                      ;Adjust D2 to hold the trapnumber.
401F68  CMPI.W  #A800,D1                   ;Is trapword smaller than A800?
401F6C  BCS  $401F88                             ;if so, then go to $401F88
401F6E  LEA  $C00,A2                              ;Now A2 points to the OS trap dispatch table.
401F72  LSL.W  #2,D2                              ;Double the trapnumber, and
401F74  MOVE.L  0(A2,D2.W),C(A7)         ;use it as an offset into the dispatch table.
                                                                ;We put the address of the trap right above  
                                                                ;the registers D1,D2,and A2 that we pushed 
                                                                ;at the start.
401F7A  CMPI.W  #AC00,D1                   ;Is the trapword smaller than AC00?
401F7E  MOVEM.L (A7)+, D1/D2/A2         ;Restore registers D1,D2, and A2.
401F82  BCS  $401F86                             ;If trapword is smaller than AC00 then go
401F84  POP.L  (A7)                                 ;Otherwise pop the trapaddress
401F86  RTS                                             ;Jump to the trap's address with the return
                                                                 ;Address on the stack.

We come here if the trapword in D1 is smaller than A800.
401F88  LEA  $400,A2
401F8C  BCLR  #8,D2
401F90  BNE  $401FAC
401F92  LSL.W  #2,D2
401F94  MOVE.L  0(A2,D2.W),A2
401F98  MOVEM.L  A0/A1,-(A7)
401F9C  JSR  (A2)
401F9E  MOVEM.L (A7)+, A0/A1
401FA2  MOVEM.L (A7)+, D1/D2/A2
401FA6  ADDQ.W  #0004,A7
401FA8  TST.W  D0
401FAA  RTS

401FAC  LSL.W  #2,D2
401FAE  MOVE.L  0(A2,D2.W),A2
401FB2  PUSH.L  A1
401FB4  JSR  (A2)
401FB6  POP.L  A1
401FB8  BRA  $401FA2

401FBA  BTST  #9,D1
401FBE  BEQ  $401FE0
401FC0  ANDI.W  #1FF,D0
401FC4  LEA  $C00,A1
401FC8  BTST  #A,D1
401FCC  BNE  $401FD6
401FCE  ANDI.W  #FF,D0
401FD2  LEA  $400,A1
401FD6  LSL.W  #2,D0
401FD8  MOVE.L  A0,0(A1,D0.W)
401FDC  MOVEQ  #0,D0
401FDE  RTS

401FE0  BSR  $401FE4
401FE2  BRA  $401FD6

401FE4  ANDI.W  #1FF,D0
401FE8  LEA  $C00,A1
401FEC  CMPI.W  #57,D0
401FF0  BHI  $402004
401FF2  BEQ  $402000
401FF4  CMPI.W  #4F,D0
401FF8  BLS  $402000
401FFA  CMPI.W  #54,D0
401FFE  BNE  $402004
402000  LEA  $400,A1
402004  RTS

402006  BSR  $401FE4
402008  BRA  $402026

40200A  BTST  #9,D1
40200E  BEQ  $402006
402010  ANDI.W  #1FF,D0
402014  LEA  $C00,A1
402018  BTST  #A,D1
40201C  BNE  $402026
40201E  ANDI.W  #FF,D0
402022  LEA  $400,A1
402026  LSL.W  #2,D0
402028  MOVE.L  0(A1,D0.W),A0
40202C  MOVEQ  #0,D0
40202E  RTS