The IDLE status flag includes logic that prevents it from getting set repeatedly when the
RxD line remains idle for an extended period of time. IDLE is cleared by reading
UARTxS1 while UART_S1[IDLE] is set and then reading UART_D. After
UART_S1[IDLE] has been cleared, it cannot become set again until the receiver has
received at least one new character and has set UART_S1[RDRF].
If the associated error was detected in the received character that caused
UART_S1[RDRF] to be set, the error flags - noise flag (UART_S1[NF]), framing error
(UART_S1[FE]), and parity error flag (UART_S1[PF]) - are set at the same time as
UART_S1[RDRF]. These flags are not set in overrun cases.
If UART_S1[RDRF] was already set when a new character is ready to be transferred
from the receive shifter to the receive data buffer, the overrun (UART_S1[OR]) flag is
set instead of the data along with any associated NF, FE, or PF condition is lost.
At any time, an active edge on the RxD serial data input pin causes the
UART_S2[RXEDGIF] flag to set. The UART_S2[RXEDGIF] flag is cleared by writing a
1 to it. This function depends on the receiver being enabled (UART_C2[RE] = 1).
40.3.5 DMA Operation
In the transmitter, flags TDRE and TC can be configured to assert a DMA transfer
request. In the receiver, flags RDRF, IDLE and LBKDIF can be configured to assert a
DMA transfer request. The following table shows the configuration bit settings required
to configure each flag for DMA operation.
Table 40-32. DMA configuration
Flag Request enable bit DMA select bit
TDRE TIE = 1 TDMAS = 1
TC TCIE = 1 TCDMAS = 1
RDRF RIE = 1 RDMAS = 1
IDLE ILIE = 1 ILDMAS = 1
LBKDIF LBKDIE = 1 LBKDDMAS = 1
When a flag is configured for a DMA request, its associated DMA request is asserted
when the flag is set. When the RDRF or IDLE flag is configured as a DMA request, the
clearing mechanism of reading UART_S1 followed by reading UART_D does not clear
the associated flag.The DMA request remains asserted until an indication is received that
the DMA transactions are done. When this indication is received, the flag bit and the
associated DMA request are cleared. If the DMA operation failed to remove the situation
that caused the DMA request another request will be issued.
Functional description
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
768 Freescale Semiconductor, Inc.
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