* set to TTY I/O number
SC    EQU 11B

      ORG 40B
LOOP  CLC 0        Turn off I/O interrupt system
      LDA TTYIO    Load A-register with control word
      OTA SC       Output control word
      STC SC,C     Set control, clear flag
WAIT  SFS SC       Wait for flag
      JMP WAIT     Loop till ready
      LIB SC       Input data word
      OTB 1        Output data word to switch register
      JMP LOOP     Next char
*TTYIO OCT 160000B   TTY input and print control word
TTYIO OCT 140000B   TTY input control word