SH7065 Datasheet, PDF (621/941 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7000 Series

Section 14 Serial Communication Interface (SCI)
SCFRDR Reading and the RDF Flag
The RDF flag in the serial status 1 register (SC1SSR) is set when the number of receive data bytes
in the receive FIFO data register (SCFRDR) has become equal to or greater than the receive
trigger number set by bits RTRG1 and RTRG0 in the FIFO control register (SCFCR). After RDF
is set, receive data equivalent to the trigger number can be read from SCFRDR, allowing efficient
continuous reception.
If the number of data bytes in SCFRDR is equal to or greater than the trigger number, the RDF
flag will be set to 1 again if it is cleared to 0. RDF should therefore be cleared to 0 after being read
as 1 after receive data has been read to reduce the number of data bytes in SCFRDR to less than
the trigger number.
The number of receive data bytes in SCFRDR can be found from the lower 8 bits of the FIFO data
count register (SCFDR).
Rev. 5.00 Sep 11, 2006 page 599 of 916
REJ09B0332-0500