Making Peter's approach even more old school, use R14 and R15 instead of R0 and R1, and do the character conversion stuff with Load Address instead of Add Halfword Immediate.
ICM R14,B'1000',BYTE Put the byte into bits 0-7 SRDL R14,30 Move BYTE.0-1 to reg 14.30-31, * zeroing reg 14.0-29 * BYTE.2-3 to reg 15.0-1 SRL R15,30 Move BYTE.2-3 to reg 15.30-31, * zeroing reg 15.0-29 LA R14,X'F1'(,R14) 0-3 => C'1'-C'4' LA R15,X'F1'(,R15) STC R14,TARGET0 STC R15,TARGET1 BYTE DS X
