Control Characters (mostly non-printing; most useful of these are highlighted in yellow.) Char... Dec Hex Description NUL 0 00 Null character SOH 1 01 Start of heading, = console interrupt STX 2 02 Start of text, maintenance mode on HP console ETX 3 03 End of text EOT 4 04 End of transmission, not the same as ETB ENQ 5 05 Enquiry, goes with ACK; old HP flow control ACK 6 06 Acknowledge, clears E..