.ORIG x3000
  ;--------------
  ; Instructions
  ;--------------

  START_LOOP
    LEA R0, PROMPT
    PUTS
    GETC
    OUT
    LD R3, CHAR_B
    ADD R4, R0, R3
    BRnp ERROR_OUT
    BRnzp CONTINUE_PROGRAM
  END_START_LOOP

  ERROR_OUT
    LEA R0, ERROR
    PUTS
    BRnzp START_LOOP
  END_ERROR_OUT

  CONTINUE_PROGRAM
    LD R1, SUB_BINARY_READER_3200
    JSRR R1
    LD R0, NEWLIN
    OUT
    JSR SUB_BINARY_WRITER_3400
  END_CONTINUE_PROGRAM

  HALT
  ;---------------
  ; Local data
  ;---------------
  PROMPT    .STRINGZ "Enter a 16-bit 2's complement binary number\n"
  ERROR     .STRINGZ "\nFirst character is not b\n"
  SUB_BINARY_READER_3200 .FILL x3200
  CHAR_B    .FILL #-98
  NEWLIN    .FILL '\n'

  ;-------------------------
  ; Subroutine
  ;-------------------------
  .ORIG x3200
  ;-------------------------
  ; Subroutine Instructions
  ;-------------------------
ST R7, BACKUP_R7_3200
  ST R1, BACKUP_R1_3200

  LD R2, TOTAl
  LD R5, COUNTER

  INPUT_LOOP_3200
    LD R4, RESET
    GETC
    OUT
    LD R3, SPACE_CHAR
    ADD R4, R0, R3
    BRz INPUT_LOOP_3200
    BRnp ZERO_INPUT

  ZERO_INPUT
    LD R4, RESET
    LD R3, ZERO
    ADD R4, R0, R3
    BRz ADD_ZERO
    BRnp ONE_INPUT

  ONE_INPUT
    LD R4, RESET
    LD R3, ONE
    ADD R4, R0, R3
    BRz ADD_ONE
    BRnp OTHER_INPUT

  OTHER_INPUT
    LEA R0, ERROR_MSG
    PUTS
    BRnzp INPUT_LOOP_3200

  ADD_ZERO
    ADD R2, R2, R2
    BRnzp INPUT_LOOP_CONT

  ADD_ONE
    ADD R2, R2, R2
    ADD R2, R2, #1
    BRnzp INPUT_LOOP_CONT

  INPUT_LOOP_CONT
    ADD R5, R5, #-1
    BRp INPUT_LOOP_3200
    BRz END_LOOP_3200

  END_LOOP_3200

    LD R1, BACKUP_R1_3200
    LD R7, BACKUP_R7_3200

  RET
  ;-----------------
  ; Subroutine data
  ;-----------------
  BACKUP_R7_3200 .BLKW #1
  BACKUP_R1_3200 .BLKW #1
  TOTAl     .FILL #0
  COUNTER   .FILL #16
  NEWLINE   .FILL '\n'
  ERROR_MSG .STRINGZ "\nEnter valid character\n"
  SPACE_CHAR    .FILL #-32

ZERO      .FILL #-48
  ONE       .FILL #-49
  RESET     .FILL #0

  ;-------------------------
  ; Subroutine
  ;-------------------------
  .ORIG x3400
  ;-------------------------
  ; Subroutine Instructions
  ;-------------------------
  SUB_BINARY_WRITER_3400
  ST R7, BACKUP_R7_3400

  LD R4, CNTR
  LD R5, SPACE_COUNTER
  LD R0, CHAR_B_3400
  OUT

  FOR_LOOP
    ADD R2, R2, #0
    BRn PRINT_1
    ADD R2, R2, #0
    BRzp PRINT_0
  END_FOR_LOOP

  PRINT_1
    LD R0, NUM_ONE
    OUT

    ADD R2, R2, R2
    ADD R4, R4, #-1
    BRz LOOP_END
    ADD R5, R5, #-1
    BRz PRINT_SPACE
    ADD R4, R4, #0
    BRp FOR_LOOP
  END_PRINT_1

  PRINT_0
    LD R0, NUM_ZERO
    OUT

    ADD R2, R2, R2
    ADD R4, R4, #-1
    BRz LOOP_END
    ADD R5, R5, #-1
    BRz PRINT_SPACE
    ADD R4, R4, #0
    BRp FOR_LOOP
  END_PRINT_0

  PRINT_SPACE
    LD R0, SPACE
    OUT
    LD R5, SPACE_COUNTER
    ;ADD R2, R2, R2
    ADD R5, R5, #0
    BRp FOR_LOOP
  END_PRINT_SPACE

LOOP_END
    LD R0, NEWLINES
    OUT

  LD R7, BACKUP_R7_3400

  RET
  ;-----------------
  ; Subroutine data
  ;-----------------
  BACKUP_R7_3400 .BLKW #1
  NUM_ZERO  .FILL #48
  NUM_ONE   .FILL #49
  CNTR      .FILL #16
  SPACE_COUNTER .FILL #4
  NEWLINES  .FILL '\n'
  SPACE     .FILL   ' '
  CHAR_B_3400   .FILL 'b'

  .end