Table of Contents
11.5 Usage Notes
Note the following points when using the SCI.
TDR Write and TDRE Flag: The TDRE flag in SSR is a status flag indicating the loading of
transmit data from TDR into TSR. The SCI sets the TDRE flag to 1 when it transfers data from
TDR to TSR.
Data can be written into TDR regardless of the state of the TDRE flag. If new data is written in
TDR when the TDRE flag is 0, the old data stored in TDR will be lost because this data has not
yet been transferred to TSR. Before writing transmit data in TDR, be sure to check that the TDRE
flag is set to 1.
Simultaneous Multiple Receive Errors: Table 11-13 indicates the state of SSR status flags when
multiple receive errors occur simultaneously. When an overrun error occurs the RSR contents are
not transferred to RDR, so receive data is lost.
Table 11-13 SSR Status Flags and Transfer of Receive Data
RDRF
1
0
0
1
1
0
1
Notes:
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Receive Data
SSR Status Flags
Transfer
RSR → RDR
ORER FER
PER
×
1
0
0
0
1
0
o
0
0
1
o
×
1
1
0
×
1
0
1
0
1
1
o
×
1
1
1
: Receive data is transferred from RSR to RDR.
o
× Receive data is not transferred from RSR to RDR.
Receive Errors
Overrun error
Framing error
Parity error
Overrun error + framing error
Overrun error + parity error
Framing error + parity error
Overrun error + framing error + parity error
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