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Part IV. Communications Processor Module
Receive commands are described in Table 21-3.
Command
After a hardware or software reset, once an SCC is enabled in the GSMR, the receiver is
ENTER HUNT
automatically enabled and uses the Þrst BD in the RxBD table. While the SCC is looking for the
MODE
beginning of a frame, that SCC is in hunt mode. The
HDLC receiver to stop receiving the current frame and enter hunt mode, in which the HDLC
continually scans the input data stream for a ßag sequence. After receiving the command, the buffer is
closed and the CRC is reset. Further frame reception uses the next BD.
Should not be used in the HDLC protocol.
CLOSE RXBD
Resets the Rx parameters in the parameter RAM.; issue only when the receiver is disabled. Note that
INIT RX
PARAMETERS
INIT TX AND RX PARAMETERS
21.7 Handling Errors in the SCC HDLC Controller
The SCC HDLC controller reports frame reception and transmission errors using BDs,
error counters, and the SCCE. Transmission errors are described in Table 21-4.
Error
Transmitter
The channel stops transmitting, closes the buffer, sets TxBD[UN], and generates a TXE interrupt if not
Underrun
masked. Transmission resumes when a
receive FIFOs are 32 bytes each.
CTS Lost
The channel stops transmitting, closes the buffer, sets TxBD[CT], and generates the TXE interrupt if
during Frame
not masked. Transmission resumes after a
Transmission
or second buffer of the frame and PSMR[RTE] = 1, the channel resends the frame when CTS is
reasserted and no error is reported. If collisions are possible, to ensure proper retransmission of multi-
buffer frames, the Þrst two buffers of each frame should in total contain more than 36 bytes for SCC or
20 bytes for SCC. The channel also increments the retransmission counter RETRC in the parameter
RAM.
Reception errors are described in Table 21-5.
Error
Overrun
Each SCC maintains an internal FIFO for receiving data. The CP begins programming the SDMA
channel (if the buffer is in external memory) and updating the CRC when a full or partial FIFOÕs worth
of data (according to GSMR_H[RFW]) is received in the Rx FIFO. When an Rx FIFO overrun occurs,
the previous byte is overwritten by the next byte. The previous data byte and the frame status are lost.
The channel closes the buffer with RxBD[OV] set and generates an RXF interrupt if not masked. The
receiver then enters hunt mode. Even if an overrun occurs during a frame whose address is not
recognized, an RxBD with data length two is opened to report the overrun and the interrupt is
generated.
CD Lost
Highest priority error. The channel stops frame reception, closes the buffer, sets RxBD[CD], and
during Frame
generates the RXF interrupt if not masked. The rest of the frame is lost and other errors are not
Reception
checked in that frame. At this point, the receiver enters hunt mode.
21-6
Table 21-3. Receive Commands
Description
resets both Tx and Rx parameters.
Table 21-4. Transmit Errors
Description
RESTART TRANSMIT
RESTART TRANSMIT
Table 21-5. Receive Errors
Description
MPC8260 PowerQUICC II UserÕs Manual
command is used to force the
ENTER HUNT MODE
command is issued. The SCC send and
command. If this error occurs on the Þrst
MOTOROLA
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