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13.5
Usage Notes
13.5.1
Notes on Use of SCI
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 to 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 13.13 shows the state of the 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 13.13 SSR Status Flags and Transfer of Receive Data
RDRF
ORER
1
1
0
0
0
0
1
1
1
1
0
0
1
1
SSR Status Flags
FER
0
1
0
1
0
1
1
Receive Data
Transfer
RSR → RDR
PER
0
Not transferred Overrun error
0
Transferred
1
Transferred
0
Not transferred Overrun error +
1
Not transferred Overrun error +
1
Transferred
1
Not transferred Overrun error +
Receive Errors
Framing error
Parity error
framing error
parity error
Framing error +
parity error
framing error +
parity error
483
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