X,Y,Z
X-Modem 58
XMIT 20, 64, 72, 81-83
XON/XOFF 3, 6-8, 11, 16, 20, 28, 31, 36, 38, 41, 49, 60, 62, 64, 67, 80-83, 116, 140
XON/XOFF handshaking 11, 36, 38, 41, 62, 64, 80
