Error-Handling Procedure; Receive Buffer Descriptor (Rx Bd) - Motorola MC68302 User Manual

mode register. If MODE1-MODEO
=
10, the synchronous link DDCMP protocol
is selected. The V.110 bit should also be set in the DDCMP mode register.
The V.110 controller uses the same basic data structure as the DDCMP con-
troller, the same command set, and the same event and mask registers for
interrupt generation.
4.5.15.6 V.110 ERROR-HANDLING PROCEDURE. The V.110 controller reports frame
reception and transmission error conditions using the channel buffer de-
scriptors (BDs) and the V.110 event register.
Transmission Errors:
1. Transmitter Underrun. When this error occurs, the channel terminates
buffer transmission, closes the buffer, sets the underrun (UN) bit in the
BD, and generates the transmit error (TXE) interrupt (if enabled). The
channel will resume transmission after the reception of the RESTART
TRANSMIT command.
Reception Errors:
1. Overrun Error. The V.110 controller maintains an internal two-byte length
FIFO for receiving data. When the receive FIFO overrun error occurs,
the channel writes the received data byte to the internal FIFO on top of
the previously received byte (the previous data byte is lost). Then the
channel closes the buffer, sets the overflow (OV) bit in the BD, and
generates the receive frame (RXF) interrupt (if enabled). The channel
will automatically enter hunt mode.
2. Synchronization Error. A synchronization error is detected by the V.110
controller when the MSB of every byte is not one. When this error occurs,
the channel writes the received byte to the buffer and continues to
receive the V.110 frame. When the frame ends, the channel closes the
buffer, sets the synchronization error (SE) bit in the BD, and generates
the RXF interrupt (if enabled). The channel will automatically enter the
hunt mode.
4.5.15.7 V.110 RECEIVE BUFFER DESCRIPTOR (Rx BO). The CP reports informa-
tion about the received data for each buffer using the BDs. The Rx BD is
shown in Figure 4-21. The CP closes the current buffer, generates a maskable
MOTOROLA MC68302 USER'S MANUAL
4-105