RRD - Z80 instruction reference

rrdRotate digit right 
Rotates the low nibble of A and both nibbles of (HL) right by one digit, leaving the high nibble of A unchanged.
2 bytes · 18 cycles
SZHP/VNC ●●0●0–
● set from the result
0 always 0
– not changed
Forms  rrd  
The contents of the low-order nibble of (HL) are copied to the low-order nibble of A. The previous contents are copied to the high-order nibble of (HL). The previous contents are copied to the low-order nibble of (HL).
         .org 0x8000
        ld hl, source
        ld a, 0x12
        rrd
        halt
source: .byte 0x34