SH7730 Datasheet, PDF (759/1188 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7780 Series

Section 22 Serial Communication Interface with FIFO (SCIF)
22.6 Usage Notes
Note the following when using the SCIF.
22.6.1 SCFTDR Writing and TDFE Flag
The TDFE flag in SCFSR is set when the number of transmit data bytes written in SCFTDR has
fallen below the transmit trigger number set by bits TTRG[1:0] in 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 ascertained through SCFDR.
22.6.2 SCFRDR Reading and RDF Flag
The RDF flag in SCFSR is set when the number of receive data bytes in SCFRDR has become
equal to or greater than the receive trigger number set by bits RTRG[1:0] in 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 SCFRDR which is less than the trigger
number.
The number of receive data bytes in SCFRDR can be ascertained through SCFDR.
22.6.3 Receive Data Sampling Timing and Receive Margin (Asynchronous Mode)
The SCIF operates on a base clock with a frequency 16 times the bit rate. In reception, the SCIF
synchronizes internally with the fall of the start bit, which it samples on the base clock. Receive
data is latched at the rising edge of the eighth base clock pulse. This is shown in figure 22.19.
Rev. 1.00 Sep. 19, 2007 Page 711 of 1136
REJ09B0359-0100