Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 702

Powerquicc family

Table of Contents

SCC HDLC Mode

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

The channel stops transmitting, closes the buffer, sets TxBD[UN], and generates a TXE interrupt if

not masked. Transmission resumes when a

transmit and receive FIFOs are 16 bytes each.

CTS Lost during

The channel stops transmitting, closes the buffer, sets TxBD[CT], and generates the TXE interrupt

if not masked. Transmission resumes after a

Transmission

first 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 first two buffers of each frame should in total contain more than 20 bytes for

SCC2–SCC4. The channel also increments the retransmission counter RETRC in the parameter

Reception errors are described in

Each SCC maintains an internal FIFO for receiving data. The CPM begins programming the SDMA

channel (if the buffer is in external memory) and updating the CRC when a full or partial FIFO's 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

CD Lost during

Highest priority error. The channel stops frame reception, closes the buffer, sets RxBD[CD], and

generates the RXF interrupt if not masked. The rest of the frame is lost and other errors are not

checked in that frame. At this point, the receiver enters hunt mode.

Abort Sequence Occurs when seven or more consecutive ones are received. When this occurs while receiving a

frame, the channel closes the buffer, sets RxBD[AB] and generates a maskable RXF interrupt. The

channel also increments the abort sequence counter ABTSC. The CRC and nonoctet error status

conditions are not checked on aborted frames. The receiver then enters hunt mode.

Table 23-4. Transmit Errors

Table 23-5. Receive Errors

MPC885 PowerQUICC Family Reference Manual, Rev. 2

command is issued. The SCC

RESTART TRANSMIT

command. If this error occurs on the

RESTART TRANSMIT

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