HD6473837H Datasheet, PDF (275/562 Pages) Renesas Technology Corp – Hardware Manual

The serial status register (SSR) is an 8-bit register containing status flags for indicating SCI3
states, and containing the multiprocessor bits.
SSR can be read and written by the CPU at any time, but the CPU cannot write a 1 to the status
flags TDRE, RDRF, OER, PER, and FER. To clear these flags to 0 it is first necessary to read a 1.
Bit 2 (TEND) and bit 1 (MPBR) are read-only bits and cannot be modified.
SSR is initialized to H'84 upon reset or in standby mode, watch mode, subactive mode, or
subsleep mode.
Bit 7—Transmit Data Register Empty (TDRE): Bit 7 is a status flag indicating that data has
been transferred from TDR to TSR.
Bit 7: TDRE
0
1
Description
Indicates that transmit data written to TDR has not been transferred to TSR
Clearing conditions:
After reading TDRE = 1, cleared by writing 0 to TDRE.
When data is written to TDR by an instruction.
Indicates that no transmit data has been written to TDR, or the transmit data
written to TDR has been transferred to TSR
(initial value)
Setting conditions:
When bit TE in SCR3 is cleared to 0.
When data is transferred from TDR to TSR.
Bit 6—Receive Data Register Full (RDRF): Bit 6 is a status flag indicating whether there is
receive data in RDR.
Bit 6: RDRF
Description
0
Indicates there is no receive data in RDR
(initial value)
Clearing conditions:
After reading RDRF = 1, cleared by writing 0 to RDRF.
When data is read from RDR by an instruction.
1
Indicates that there is receive data in RDR
Setting condition:
When receiving ends normally, with receive data transferred from RSR to RDR
Note:
If a receive error is detected at the end of receiving, or if bit RE in serial control register 3
(SCR3) is cleared to 0, RDR and RDRF are unaffected and keep their previous states. An
overrun error (OER) occurs if receiving of data is completed while bit RDRF remains set
to 1. If this happens, receive data will be lost.
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