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MOTOROLA
Chapter 22. SCC UART Mode
22-13
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Handling Errors in the SCC UART Controller
Table 22-7. Transmission Errors
Error
Description
CTS Lost during
Character
Transmission
When CTS negates during transmission, the channel stops after nishing 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 ow 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.
Framing
The UART reports a framing errors when it receives a character with no stop bit, regardless of the
mode. The channel writes the received character to the buffer, closes it, sets RxBD[FR], generates
the RX interrupt if not masked, increments FRMEC, but does not check parity for this character. In
automatic multidrop mode, the receiver immediately enters hunt mode. If the UART allows data with
no stop bits (PSMR[RZS] = 1) when in synchronous mode (PSMR[SYN] = 1), framing errors are
reported but reception continues assuming the unexpected zero is the start bit of the next character;
in this case, the user may ignore a reported framing error until multiple framing errors occur within a
short period.
Break Sequence When the rst break sequence is received, the UART increments the break error counter BRKEC. It
updates BRKLN when the sequence completes. After the rst 1 is received, the UART sets
SCCE[BRKE], which generates an interrupt if not masked. If the UART is receiving characters when
it receives a break, it closes the Rx buffer, sets RxBD[BR], and sets SCCE[RX], which can generate
an interrupt if not masked. If PSMR[RZS] = 1 when the UART is in synchronous mode, a break
sequence is detected after two successive break characters are received.