H8-3048B Datasheet, PDF (535/901 Pages) Renesas Technology Corp – 8-Bit Single-Chip Microcomputer

13.5 Usage Notes
Note the following points when using the SCI.
Section 13 Serial Communication Interface
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 13.13 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 13.13 SSR Status Flags and Transfer of Receive Data
SSR Status Flags
RDRF ORER FER PER
Receive Data
Transfer
RSR → RDR
Receive Errors
1
1
0
0
×
Overrun error
0
0
1
0
O
Framing error
0
0
0
1
O
Parity error
1
1
1
0
×
Overrun error + framing error
1
1
0
1
×
Overrun error + parity error
0
0
1
1
O
Framing error + parity error
1
1
1
1
×
Overrun error + framing error + parity error
Legend:
O: Receive data is transferred from RSR to RDR.
×: Receive data is not transferred from RSR to RDR.
Rev. 3.00 Sep 27, 2006 page 509 of 872
REJ09B0325-0300