mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 1132

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

Application information
43.8.4.1 Overrun operation
The assertion of the S1[OR] flag indicates that a significant event has occurred. The
assertion indicates that received data has been lost since there was a lack of room to store
it in the data buffer. Hence, while the S1[OR] flag is set no further data will be stored in
the data buffer until the S1[OR] flag is cleared. This ensures that the application will be
able to handle the overrun condition.
In most applications since the total amount of lost data is known, the application will
desire to return the system to a known state. Prior to the S1[OR] flag being cleared all
received data will be dropped. To do this the software would:
Note that in some applications if an overrun event is responded to fast enough, the lost
data can be recovered. For example when C7816[ISO_7816E] is asserted,
C7816[TTYPE]=1 and C7816[ONACK] = 1 the application may reasonably be able to
determine if the lost data will be resent by the device. In this scenario flushing the
receiver data buffer might not be required. Rather, if the S1[OR] flag is cleared the lost
data may be resent and hence recoverable.
When LIN break detect (LBKDE) is asserted the S1[OR] flag has significantly different
behavior than in other modes. The S1[OR] bit will be set, regardless of how much space
is actually available in the data buffer, if a LIN break character has been detected and the
corresponding flag (S2[LBKDIF]) is not cleared before the first data character is received
after the S2[LBKDIF] asserted. This behavior is intended to allow software sufficient
time to read the LIN break character from the data buffer to ensure that a break character
was actually detected. The checking of the break character was used on some older
implementations and is hence supported for legacy reasons. Applications that do not
require this checking can simply clear the S2[LBKDIF] without checking the stored value
to ensure it is a break character.
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1. Remove data from the receive data buffer. This could be done by reading data from
2. Clear the S1[OR] flag. Note that if data was cleared using the CFIFO[RXFLUSH]
the data buffer and processing it if the data in the FIFO was still valuable when
though the overrun event occurred or using the CFIFO[RXFLUSH] bit to clear the
buffer.
bit, then clearing the S1[OR] flag will result in the SFIFO[RXUF] flag asserting
because the only way to clear the S1[OR] requires reading additional information
from the FIFO. Care should be taken to disable the SFIFO[RXUF] interrupt prior to
clearing the OR flag and then clearing the SFIFO[RXUF] flag after the OR flag has
been cleared.
MCF51JF128 Reference Manual, Rev. 2, 03/2011
Preliminary
Freescale Semiconductor, Inc.