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Reception errors are described in Table 20-8.
Error
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
If this error occurs and the channel is using this pin to automatically control reception, the channel
during
terminates character reception, closes the buffer, sets RxBD[CD], and generates the RX interrupt if not
Character
masked. This error has the highest priority. The last character in the buffer is lost and other errors are not
Reception
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
If the UART is receiving data and gets an idle character (all ones), the channel begins counting
Sequence
consecutive idle characters received. If MAX_IDL is reached, the buffer is closed and an RX interrupt is
Receive
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
When the Þrst break sequence is received, the UART increments the break error counter BRKEC. It
Sequence
updates BRKLN when the sequence completes. After the Þrst 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.
20.16 UART Mode Register (PSMR)
For UART mode, the SCC protocol-speciÞc mode register (PSMR) is called the UART
mode register. Many bits can be modiÞed while the receiver and transmitter are enabled.
Figure 20-6 shows the PSMR in UART mode.
MOTOROLA
Table 20-8. Reception Errors
Description
Chapter 20. SCC UART Mode
Part IV. Communications Processor Module
20-13
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