MOTOROLA
Chapter 15. Queued Serial Multi-Channel Module
15-53
Serial Communication Interface
15.7.5
SCI Data Register (SCxDR)
The SCxDR consists of two data registers located at the same address. The receive data
register (RDRx) is a read-only register that contains data received by the SCI serial
interface. Data is shifted into the receive serial shifter and is transferred to RDRx. The
11
IDLE
Idle line detected. IDLE is set when the receiver detects an idle-line condition (reception of a
minimum of 10 or 11 consecutive ones as specified by ILT in SCCxR1). This bit is not set by the
idle-line condition when RWU in SCCxR1 is set. Once cleared, IDLE is not set again until after
RDRF is set (after the line is active and becomes idle again). If a break is received, RDRF is set,
allowing a subsequent idle line to be detected again.
Under certain conditions, the IDLE flag may be set immediately following the negation of RE in
SCCxR1. System designs should ensure this causes no detrimental effects.
0 SCI receiver did not detect an idle-line condition.
1 SCI receiver detected an idle-line condition.
For receiver queue operation, IDLE is cleared when SCxSR is read with IDLE set, followed by a
read of SCRQ[0:15].
12
OR
Overrun error. OR is set when a new byte is ready to be transferred from the receive serial shifter
to register RDRx, and RDRx is already full (RDRF is still set). Data transfer is inhibited until OR
is cleared. Previous data in RDRx remains valid, but additional data received during an overrun
condition (including the byte that set OR) is lost.
Note that whereas the other receiver status flags (NF, FE, and PF) reflect the status of data
already transferred to RDRx, the OR flag reflects an operational condition that resulted in a loss
of data to RDRx.
0 RDRF is cleared before new data arrives.
1 RDRF is not cleared before new data arrives.
13
NF
Noise error flag. NF is set when the receiver detects noise on a valid start bit, on any of the data
bits, or on the stop bit(s). It is not set by noise on the idle line or on invalid start bits. Each bit is
sampled three times for noise. If the three samples are not at the same logic level, the majority
value is used for the received data value, and NF is set. NF is not set until the entire frame is
received and RDRF is set.
Although no interrupt is explicitly associated with NF, an interrupt can be generated with RDRF,
and the interrupt handler can check NF.
0 No noise detected in the received data.
1 Noise detected in the received data.
For receiver queue operation NF is cleared when SCxSR is read with NF set, followed by a read
of SCRQ[0:15].
14
FE
Framing error. FE is set when the receiver detects a zero where a stop bit (one) was expected.
A framing error results when the frame boundaries in the received bit stream are not synchronized
with the receiver bit counter. FE is not set until the entire frame is received and RDRF is set.
Although no interrupt is explicitly associated with FE, an interrupt can be generated with RDRF,
and the interrupt handler can check FE.
0 No framing error detected in the received data.
1 Framing error or break detected in the received data.
15
PF
Parity error. PF is set when the receiver detects a parity error. PF is not set until the entire frame
is received and RDRF is set.
Although no interrupt is explicitly associated with PF, an interrupt can be generated with RDRF,
and the interrupt handler can check PF.
0 No parity error detected in the received data.
1 Parity error detected in the received data.
Table 15-26. SCxSR Bit Descriptions (continued)
Bits
Name
Description