
GT-96100A Advanced Communication Controller
Revision 1.0
349
14.6.2.2 BISYNC Auto Transparent Receive Mode
In Auto Transparent Mode, the BISYNC receiver handles the following protocol functions:
BISYNC, MonoSYNC, NibbleSYNC, or External SYNC synchronization.
Auto SYNC stripping in text mode.
Auto DLE-SYNC stripping in transparent text mode.
Auto SYNC stripping after receiving DLE ITB in transparent mode.
Automatic switch to transparent mode after receiving DLE-STX.
Automatic exit of transparent mode after receiving DLE-ETX/ETB.
Marking of buffers that contain transparent data by setting the TB bit in the descriptor.
BCC generation:
- BCC (CRC-16, VRC/LRC and VRC/CRC-16) is calculated.
- In transparent text mode, CRC-16 always overrides the VRC.
- SYNC (DLE-SYNC) is not included in the BCC calculation.
- Opening STX/SOH (DLE-STX) are discarded from BCC calculations.
Buffer closing at the reception of ETX, ETB, ITB, and ENQ.
Maintaining SYNC (stay in text mode) after ITB.
Buffer closing after SYN-SYN-DLE-CHAR (when char is not STX).
Protocol correctness checking:
- Test for ‘1’ padding at the end of block reception. (The CPU should ignore a padding error reported
after ITB, and can use it when testing for proper NAK or EOT.)
- Test for DLE-CTL (CTL is a control character with B or H set) after receiving DLE-ITB in
transparent text mode. If another sequence arrives (except SYNCs), buffer is closed with a DLE
error.
The BISYNC receive process is block oriented. A block starts after a buffer was closed due to control character
reception, overrun, protocol error, parity error, or line error (i.e. CD deassertion).
The first descriptor in a block is marked with F bit set to ‘1’. The last descriptor in block is marked with L bit set
to ‘1’. The last descriptor also includes the actual status report for the block. Intermediate descriptors can be rec-
ognized by having both F and L bit set to ‘0’.