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MCF51QE128 MCU Series Reference Manual, Rev. 3
Freescale Semiconductor 303
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15.2.5 SCI Status Register 2 (SCIxS2)
This register contains one read-only status flag.
When using an internal oscillator in a LIN system, it is necessary to raise the break detection threshold one
bit time. Under the worst case timing conditions allowed in LIN, it is possible that a 0x00 data character
can appear to be 10.26 bit times long at a slave running 14% faster than the master. This would trigger
normal break detection circuitry designed to detect a 10-bit break symbol. When the LBKDE bit is set,
76543210
R
LBKDIF RXEDGIF
0
RXINV RWUID BRK13 LBKDE
RAF
W
Reset00000000
Figure 15-10. SCI Status Register 2 (SCIxS2)
Table 15-6. SCIxS2 Field Descriptions
Field Description
7
LBKDIF
LIN Break Detect Interrupt Flag. LBKDIF is set when the LIN break detect circuitry is enabled and a LIN break
character is detected. LBKDIF is cleared by writing a 1 to it.
0 No LIN break character has been detected.
1 LIN break character has been detected.
6
RXEDGIF
RxD Pin Active Edge Interrupt Flag. RXEDGIF is set when an active edge (falling if RXINV = 0, rising if RXINV=1)
on the RxD pin occurs. RXEDGIF is cleared by writing a 1 to it.
0 No active edge on the receive pin has occurred.
1 An active edge on the receive pin has occurred.
4
RXINV
1
1
Setting RXINV inverts the RxD input for all cases: data bits, start and stop bits, break, and idle.
Receive Data Inversion. Setting this bit reverses the polarity of the received data input.
0 Receive data not inverted
1 Receive data inverted
3
RWUID
Receive Wake Up Idle Detect. RWUID controls whether the idle character that wakes up the receiver sets the
IDLE bit.
0 During receive standby state (RWU = 1), the IDLE bit does not get set upon detection of an idle character.
1 During receive standby state (RWU = 1), the IDLE bit gets set upon detection of an idle character.
2
BRK13
Break Character Generation Length. BRK13 selects a longer transmitted break character length. Detection of a
framing error is not affected by the state of this bit.
0 Break character is transmitted with length of 10 bit times (11 if M = 1)
1 Break character is transmitted with length of 13 bit times (14 if M = 1)
1
LBKDE
LIN Break Detection Enable. LBKDE selects a longer break character detection length. While LBKDE is set,
framing error (FE) and receive data register full (RDRF) flags are prevented from setting.
0 Break character is detected at length of 10 bit times (11 if M = 1).
1 Break character is detected at length of 11 bit times (12 if M = 1).
0
RAF
Receiver Active Flag. RAF is set when the SCI receiver detects the beginning of a valid start bit, and RAF is
cleared automatically when the receiver detects an idle line. This status flag can be used to check whether an
SCI character is being received before instructing the MCU to go to stop mode.
0 SCI receiver idle waiting for a start bit.
1 SCI receiver active (RxD input not idle).