Freescale Semiconductor PowerQUICC MPC870, Reference Manual

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SCC UART Mode
MPC885 PowerQUICC Family Reference Manual, Rev. 2
22-12 Freescale Semiconductor
22.15 Handling Errors in the SCC UART Controller
The UART controller reports character reception and transmission error conditions via the BDs, the error
counters, and the SCCE. Modem interface lines can be monitored by the port C pins. Transmission errors
are described in
Table 22-7 .
Reception errors are described in Table 22-8 .
Table 22-7. Transmission Errors
Error Description
CTS Lost during
Character
Transmission
When CTS negates during transmission, the channel stops after finishing the current character. The
CP sets TxBD[CT] and generates the TX interrupt if it is not masked. The channel resumes
transmission after the
RESTART TRANSMIT
command is issued and CTS is asserted.
Note that if CTS is used, the UART also offers an asynchronous flow control option that does not
generate an error. See the description of PSMR[FLC] in
Table 22-9 .
Table 22-8. Reception Errors
Error Description
Overrun Occurs when the channel overwrites the previous character in the Rx FIFO with a new character,
losing the previous character. The channel then writes the new character to the buffer, closes it, sets
RxBD[OV], and generates an RX interrupt if not masked. In automatic multidrop mode, the receiver
enters hunt mode immediately.
CD Lost during
Character
Reception
If this error occurs and the channel is using this pin to automatically control reception, the channel
terminates character reception, closes the buffer, sets RxBD[CD], and generates the RX interrupt if
not masked. This error has the highest priority. The last character in the buffer is lost and other errors
are not checked. In automatic multidrop mode, the receiver enters the hunt mode immediately.
Parity When a parity error occurs, the channel writes the received character to the buffer, closes the buffer,
sets RxBD[PR], and generates the RX interrupt if not masked. The channel also increments the
parity error counter PAREC. In automatic multidrop mode, the receiver enters hunt mode
immediately.
Noise A noise error occurs when the three samples of a bit are not identical. When this error occurs, the
channel writes the received character to the buffer, proceeds normally, but increments the noise
error counter NOSEC. Note that this error does not occur in synchronous mode.
Idle Sequence
Receive
If the UART is receiving data and gets an idle character (all ones), the channel begins counting
consecutive idle characters received. If MAX_IDL is reached, the buffer is closed and an RX
interrupt is generated if not masked. If no buffer is open, this event does not generate an interrupt
or any status information. The internal idle counter (IDLC) is reset every time a character is received.
To disable the idle sequence function, clear MAX_IDL.