Table of Contents
Advertisement
This error can occur only on synchronous links.
2. Clear-To-Send Lost (Collision) During Message Transmission. When this error occurs
and the channel is not programmed to control this line with software, the channel ter-
minates buffer transmission, closes the buffer, sets the CTS lost (CT) bit in the BD,
and generates the transmit error (TXE) interrupt (if enabled). The channel resumes
transmission after the reception of the RESTART TRANSMIT command.
Reception Errors:
1. Carrier Detect Lost During Message Reception. When this error occurs and the chan-
nel is not programmed to control this line with software, the channel terminates mes-
sage reception, closes the buffer, sets the carrier detect lost (CD) bit in the BD, and
generates the receive block (RBK) interrupt (if enabled). This error has the highest pri-
ority. The rest of the message is lost, and other errors in that message are not
checked.
The channel will enter hunt mode immediately. It is possible that a SYN1–SYN2-
(SOH,DLE,ENQ) sequence in data will be incorrectly interpreted as the start of the
next header, but this "header" will have a CRC error.
2. Overrun Error. The DDCMP controller maintains an internal three-byte FIFO for re-
ceiving data. The CP begins programming the SDMA channel (if the data buffer is in
external memory) and updating the CRC when the first word is received into the FIFO.
If 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 overrun (OV) bit in the BD, and generates
the receive block (RBK) interrupt (if enabled).
The channel will enter hunt mode immediately. It is possible that a SYN1–SYN2-
(SOH,DLE,ENQ) sequence in data will be incorrectly interpreted as the start of the
next header, but this "header" will have a CRC error.
3. CRC1 (Header CRC) Error. When this error occurs, the channel writes the received
CRC to the data buffer, closes the buffer, sets the CRC error (CR) bit in the BD, gen-
erates the RBK interrupt (if enabled), increments the error counter (CRC1EC), and en-
ters hunt mode.
When this error occurs on data-and maintenance-message header fields, the channel
will enter hunt mode immediately. It is possible that a SYN1–SYN2-(SOH,DLE,ENQ)
sequence in data will be incorrectly interpreted as the start of the next header, but this
"header" will have a CRC error.
4. CRC2 (Data or Maintenance CRC) or CRC3 (Control Message) Error. When this error
occurs, the channel writes the received CRC to the data buffer, closes the buffer, sets
the CRC error (CR) bit in the BD, and generates the RBK interrupt (if enabled). The
channel also increments the CRC2EC counter and enters hunt mode.
5. Framing Error. A framing error is detected by the DDCMP controller when no stop bit
is detected in a received data string. When this error occurs, the channel writes the
received character to the buffer, closes the buffer, sets the framing error (FR) bit in the
BD, and generates the RBK interrupt (if enabled). When this error occurs, parity is not
checked for this character.
MOTOROLA
NOTE
MC68302 USER'S MANUAL
Communications Processor (CP)
4-107
Advertisement
Table of Contents
