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Section 15 Serial Communication Interface with FIFO
R01UH0134EJ0400 Rev. 4.00 Page 771 of 2108
Sep 24, 2014
SH7262 Group, SH7264 Group
15.6 Usage Notes
Note the following when using this module.
15.6.1 SCFTDR Writing and TDFE Flag
The TDFE flag in the serial status register (SCFSR) is set when the number of transmit data bytes
written in the transmit FIFO data register (SCFTDR) has fallen below the transmit trigger number
set by bits TTRG[1:0] in the FIFO control register (SCFCR). After the TDFE flag is set, transmit
data up to the number of empty bytes in SCFTDR can be written, allowing efficient continuous
transmission.
However, if the number of data bytes written in SCFTDR is equal to or less than the transmit
trigger number, the TDFE flag will be set to 1 again after being read as 1 and cleared to 0. TDFE
flag clearing should therefore be carried out when SCFTDR contains more than the transmit
trigger number of transmit data bytes.
The number of transmit data bytes in SCFTDR can be found from the upper 8 bits of the FIFO
data count register (SCFDR).
15.6.2 SCFRDR Reading and RDF Flag
The RDF flag in the serial status register (SCFSR) 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 RTRG[1:0] in the FIFO control register (SCFCR). After RDF flag is set,
receive data equivalent to the trigger number can be read from SCFRDR, allowing efficient
continuous reception.
However, if the number of data bytes in SCFRDR exceeds the trigger number, the RDF flag will
be set to 1 again if it is cleared to 0. The RDF flag should therefore be cleared to 0 after being read
as 1 after reading the number of the received data in the receive FIFO data register (SCFRDR)
which is 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).