MPC8280 datasheet(736/1386 Pages) FREESCALE

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SCC HDLC Mode

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

22-6

Freescale Semiconductor

22.7

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 22-4.

Reception errors are described in Table 22-5.

Table 22-4. Transmit Errors

Error

Description

Transmitter

Underrun

The channel stops transmitting, closes the buffer, sets TxBD[UN], and generates a TXE interrupt if not

masked. Transmission resumes when a RESTART TRANSMIT command is issued. The SCC send and

receive FIFOs are 32 bytes each.

CTS Lost

during Frame

Transmission

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

not masked. Transmission resumes after a RESTART TRANSMIT command. If this error occurs on the

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 36 bytes for

SCC or 20 bytes for SCC. The channel also increments the retransmission counter RETRC in the

parameter RAM.

Table 22-5. Receive Errors

Error

Description

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 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

generated.

CD Lost

during

Frame

Reception

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.

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