Chapter 11 Serial Communication Interface (S12SCIV5)
MC9S12XDP512 Data Sheet, Rev. 2.17
490
Freescale Semiconductor
3
OR
Overrun Flag — OR is set when software fails to read the SCI data register before the receive shift register
receives the next frame. The OR bit is set immediately after the stop bit has been completely received for the
second frame. The data in the shift register is lost, but the data already in the SCI data registers is not affected.
Clear OR by reading SCI status register 1 (SCISR1) with OR set and then reading SCI data register low
(SCIDRL).
0 No overrun
1 Overrun
Note: OR ag may read back as set when RDRF ag is clear. This may happen if the following sequence of
events occurs:
1. After the rst frame is received, read status register SCISR1 (returns RDRF set and OR ag clear);
2. Receive second frame without reading the rst frame in the data register (the second frame is not
received and OR ag is set);
3. Read data register SCIDRL (returns rst frame and clears RDRF ag in the status register);
4. Read status register SCISR1 (returns RDRF clear and OR set).
Event 3 may be at exactly the same time as event 2 or any time after. When this happens, a dummy
SCIDRL read following event 4 will be required to clear the OR ag if further frames are to be received.
2
NF
Noise Flag — NF is set when the SCI detects noise on the receiver input. NF bit is set during the same cycle as
the RDRF ag but does not get set in the case of an overrun. Clear NF by reading SCI status register 1(SCISR1),
and then reading SCI data register low (SCIDRL).
0 No noise
1 Noise
1
FE
Framing Error Flag — FE is set when a logic 0 is accepted as the stop bit. FE bit is set during the same cycle
as the RDRF ag but does not get set in the case of an overrun. FE inhibits further data reception until it is
cleared. Clear FE by reading SCI status register 1 (SCISR1) with FE set and then reading the SCI data register
low (SCIDRL).
0 No framing error
1 Framing error
0
PF
Parity Error Flag — PF is set when the parity enable bit (PE) is set and the parity of the received data does not
match the parity type bit (PT). PF bit is set during the same cycle as the RDRF ag but does not get set in the
case of an overrun. Clear PF by reading SCI status register 1 (SCISR1), and then reading SCI data register low
(SCIDRL).
0 No parity error
1 Parity error
Table 11-10. SCISR1 Field Descriptions (continued)
Field
Description