Exception Handling and Synchronisation

Several situations are considered exceptions from normal operation of the TPI. When the TPI physical layer is in receive mode, these exceptions are:

The TPI physical layer detects a parity error.
The TPI physical layer detects a frame error.
The TPI physical layer recognizes a BREAK character.

When the TPI physical layer is in transmit mode, the possible exceptions are:

The TPI physical layer detects a data collision.

All these exceptions are signalized to the TPI access layer. The access layer responds to an exception by aborting any on-going operation and enters the error state. The access layer will stay in the error state until a BREAK character has been received, after which it is taken back to its default state. As a consequence, the external programmer can always synchronize the protocol by simply transmitting two successive BREAK characters.