
Serial Communications Interface (SCI)
SCI Registers
M68HC11E Family — Rev. 5
Data Sheet
MOTOROLA
Serial Communications Interface (SCI)
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125
7.7.4  Serial Communication Status Register 
The SCSR provides inputs to the interrupt logic circuits for generation of the SCI 
system interrupt.
TDRE — Transmit Data Register Empty Flag 
This flag is set when SCDR is empty. Clear the TDRE flag by reading SCSR with 
TDRE set and then writing to SCDR. 
0 = SCDR busy 
0 = SCDR empty 
TC — Transmit Complete Flag 
This flag is set when the transmitter is idle (no data, preamble, or break 
transmission in progress). Clear the TC flag by reading SCSR with TC set and 
then writing to SCDR. 
0 = Transmitter busy 
1 = Transmitter idle 
RDRF — Receive Data Register Full Flag 
This flag is set if a received character is ready to be read from SCDR. Clear the 
RDRF flag by reading SCSR with RDRF set and then reading SCDR. 
0 = SCDR empty 
1 = SCDR full 
IDLE — Idle Line Detected Flag 
This flag is set if the RxD line is idle. Once cleared, IDLE is not set again until 
the RxD line has been active and becomes idle again. The IDLE flag is inhibited 
when RWU = 1. Clear IDLE by reading SCSR with IDLE set and then reading 
SCDR. 
0 = RxD line active 
1 = RxD line idle 
OR — Overrun Error Flag 
OR is set if a new character is received before a previously received character 
is read from SCDR. Clear the OR flag by reading SCSR with OR set and then 
reading SCDR. 
0 = No overrun 
1 = Overrun detected 
Address:
$102E
Bit 7
6
5
4
3
2
1
Bit 0
Read:
TDRE
TC
RDRF
IDLE
OR
NF
FE
Write:
Reset:
1
1
0
0
0
0
0
0
= Unimplemented
Figure 7-6. Serial Communications Status Register (SCSR)
F
Freescale Semiconductor, Inc.
n
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