OS_Blp, Make a bleep

Register parameters

RST 20H, DEFW $D806

IN:
     A = sound count
     B = space count
     C = mark count
OUT:
     Fc = 0 always

Registers changed after return:
     ....DEHL/IXIY same
     AFBC..../.... different

Notes

Called as VDU 1, n, "!", ...