D4 INT D4 - IBM ROM BASIC - used while in interpreter
D4 INT D4 - STSC APL*PLUS/PC - MAY BE USED IN FUTURE RELEASES

 00    02 03 04       07                        
 10 11 12 13       16       19 1A 1B 1C 1D 1E 1F
 20 21 22 23 24 25 26 27 28 29 2A    2C 2D