Motorola MC68302 User Manual page 178

4.5.13.8 BISYNC ERROR-HANDLING PROCEDURE.
The BISYNC controller reports
message reception and transmission error conditions using the channel BDs,
the error counters, and the BISYNC event register. The modem interface lines
can also be directly monitored in the
sec
status 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 TXE interrupt (if enabled). The channel resumes
transmission after the reception of the RESTART TRANSMIT command.
Underrun cannot occur between frames.
2. Clear To Send Lost During Message Transmission. When this error oc-
curs and the channel is not programmed to control this line with soft-
ware, the channel terminates buffer transmission, closes the buffer, sets
the CTS lost (CT) bit in the BD, and generates the TXE interrupt (if
enabled). The channel will resume transmission after the reception of
the RESTART TRANSMIT command.
Reception Errors:
1. Overrun Error. The BISYNC controller maintains an internal two-byte
FIFO for receiving data. The CP begins programming the SOMA channel
(if the data buffer is in external memory) and updating the CRC when
the first word is received into the FIFO. If a FIFO overrun occurs, the
BISYNC controller writes the received data byte to the internal FIFO over
the previously received byte. The previous character and its status bits
are lost. Following this, the channel closes the buffer, sets the overrun
(OV) bit in the BD, and generates the RX interrupt (if enabled). The
receiver then enters hunt mode immediately.
2. Carrier Detect Lost During Message Reception. When this error occurs
and the channel is not programmed to control this line with software,
the channel terminates message reception, closes the buffer, sets the
carrier detect lost (CD) bit in the BD, and generates the RX interrupt (if
enabled). This error is the highest priority; the rest of the message is
lost and no other errors are checked in the message. The receiver then
enters hunt mode immediately.
3. Parity Error. When this error occurs, the channel writes the received
character to the buffer and sets the PR bit in the BD. The channel ter-
minates message reception, closes the buffer, sets the PR bit in the BD,
and generates the RX interrupt (if enabled). The channel also increments
the parity error counter (PAREC), and the receiver then enters hunt mode
immediately.
MOTOROLA
MC68302 USER'S MANUAL 4-75