OUTD - Z80 instruction reference

outdOutput and decrement 
Decrements B, writes the byte at (HL) to the port addressed by BC, then decrements HL.
2 bytes · 16 cycles
SZHP/VNC ?●??1?
● set from the result
1 always 1
? undefined afterwards
Forms  outd  
B is decremented. A byte from the memory location pointed to by HL is written to the port at the 16-bit address contained in the BC register pair. Then HL is decremented. Note that the carry flag may be affected, contrary to documentation. Read More
         .org 0x8000
        ld hl, source + 1
        ld b, 2
        ld c, 1
        outd
        halt
source: .byte 42, 7