Information
UARTx_S1 field descriptions (continued)
Field Description
0 Receiver input is either active now or has never become active since the IDLE flag was last cleared.
1 Receiver input has become idle or the flag has not been cleared since it last asserted.
3
OR
Receiver Overrun Flag
OR is set when software fails to prevent the receive data register from overflowing with data. The OR bit is
set immediately after the stop bit has been completely received for the dataword that overflows the buffer
and all the other error flags (FE, NF, and PF) are prevented from setting. The data in the shift register is
lost, but the data already in the UART data registers is not affected. If the OR flag is set, no data is stored
in the data buffer even if sufficient room exists. Additionally, while the OR flag is set, the RDRF and IDLE
flags are blocked from asserting, that is, transition from an inactive to an active state. To clear OR, read
S1 when OR is set and then read D. If LBKDE is enabled and a LIN Break is detected, the OR field
asserts if S2[LBKDIF] is not cleared before the next data character is received.See for more details
regarding the operation of the OR bit. Overrun (OR) flag implicationsIn 7816 mode, it is possible to
configure a NACK to be returned by programing C7816[ONACK].
0 No overrun has occurred since the last time the flag was cleared.
1 Overrun has occurred or the overrun flag has not been cleared since the last overrun occured.
2
NF
Noise Flag
NF is set when the UART detects noise on the receiver input. NF does not become set in the case of an
overrun or while the LIN break detect feature is enabled (S2[LBKDE] = 1). When NF is set, it indicates
only that a dataword has been received with noise since the last time it was cleared. There is no
guarantee that the first dataword read from the receive buffer has noise or that there is only one dataword
in the buffer that was received with noise unless the receive buffer has a depth of one. To clear NF, read
S1 and then read D. When EN709 is set/enabled, noise flag is not set.
0 No noise detected since the last time this flag was cleared. If the receive buffer has a depth greater
than 1 then there may be data in the receiver buffer that was received with noise.
1 At least one dataword was received with noise detected since the last time the flag was cleared.
1
FE
Framing Error Flag
FE is set when a logic 0 is accepted as the stop bit. FE does not set in the case of an overrun or while the
LIN break detect feature is enabled (S2[LBKDE] = 1). FE inhibits further data reception until it is cleared.
To clear FE, read S1 with FE set and then read D. The last data in the receive buffer represents the data
that was received with the frame error enabled. Framing errors are not supported when 7816E is set/
enabled. However, if this flag is set, data is still not received in 7816 mode.Framing errors are not
supported in 709 mode.
0 No framing error detected.
1 Framing error.
0
PF
Parity Error Flag
PF is set when PE is set, S2[LBKDE] is disabled, and the parity of the received data does not match its
parity bit. The PF is not set in the case of an overrun condition. When PF is set, it indicates only that a
dataword was received with parity error since the last time it was cleared. There is no guarantee that the
first dataword read from the receive buffer has a parity error or that there is only one dataword in the buffer
that was received with a parity error, unless the receive buffer has a depth of one. To clear PF, read S1
and then read D. Within the receive buffer structure the received dataword is tagged if it is received with a
parity error. This information is available by reading the ED register prior to reading the D register.When
EN709 is set/enabled parity error flag is not set.
0 No parity error detected since the last time this flag was cleared. If the receive buffer has a depth
greater than 1, then there may be data in the receive buffer what was received with a parity error.
1 At least one dataword was received with a parity error since the last time this flag was cleared.
Chapter 48 Universal Asynchronous Receiver/Transmitter (UART)
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
Freescale Semiconductor, Inc.
Preliminary
1287
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