Up: The Optical Link
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The optical link monitors itself for errors in several ways;
- Parity Checking The parity of each byte decoded is checked
against the parity bit contained in the control byte. If a mis-match
occurs, the OLD sets the PERR line to the IB .
- Running Disparity If a 10-bit character is corrupted during the
transfer it will generally not correspond to a valid code (of the 1024
possible 10-bit codes only 256 correspond to valid 8-bit words). This
will be detected and will cause the OLD to set the RDERR line.
- Sequence Error D38 is the sequence bit and this must toggle
between each word transferred. If two consecutive words have the same
value of D38 an error is detected and the SERR line is set in the OLD .
- Hardware Errors The OLC -266 is designed to detect an open fibre
connection and will set the Link Status line in this eventuality. In
addition, if the power available in the laser exceeds a maximum value a
Laser Fault line will be set.
Editor: Jean-Pol Matheys (firstname.lastname@example.org)