Datasheet

Chapter 14 Serial Communications Interface (S08SCIV4)
MC9S08SH8 MCU Series Data Sheet, Rev. 3
214 Freescale Semiconductor
When using an internal oscillator in a LIN system, it is necessary to raise the break detection threshold by
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 which is running 14% faster than the master. This
would trigger normal break detection circuitry which is designed to detect a 10 bit break symbol. When
the LBKDE bit is set, framing errors are inhibited and the break detection threshold changes from 10 bits
to 11 bits, preventing false detection of a 0x00 data character as a LIN break symbol.
14.2.6 SCI Control Register 3 (SCIxC3)
1
LBKDE
LIN Break Detection Enable— LBKDE is used to select 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).
1
Setting RXINV inverts the RxD input for all cases: data bits, start and stop bits, break, and idle.
76543210
RR8
T8 TXDIR TXINV ORIE NEIE FEIE PEIE
W
Reset 00000000
= Unimplemented or Reserved
Figure 14-10. SCI Control Register 3 (SCIxC3)
Table 14-7. SCIxC3 Field Descriptions
Field Description
7
R8
Ninth Data Bit for Receiver — When the SCI is configured for 9-bit data (M = 1), R8 can be thought of as a
ninth receive data bit to the left of the MSB of the buffered data in the SCIxD register. When reading 9-bit data,
read R8 before reading SCIxD because reading SCIxD completes automatic flag clearing sequences which
could allow R8 and SCIxD to be overwritten with new data.
6
T8
Ninth Data Bit for Transmitter — When the SCI is configured for 9-bit data (M = 1), T8 may be thought of as a
ninth transmit data bit to the left of the MSB of the data in the SCIxD register. When writing 9-bit data, the entire
9-bit value is transferred to the SCI shift register after SCIxD is written so T8 should be written (if it needs to
change from its previous value) before SCIxD is written. If T8 does not need to change in the new value (such
as when it is used to generate mark or space parity), it need not be written each time SCIxD is written.
5
TXDIR
TxD Pin Direction in Single-Wire Mode — When the SCI is configured for single-wire half-duplex operation
(LOOPS = RSRC = 1), this bit determines the direction of data at the TxD pin.
0 TxD pin is an input in single-wire mode.
1 TxD pin is an output in single-wire mode.
Table 14-6. SCIxS2 Field Descriptions (continued)
Field Description