SH7065 Datasheet, PDF (582/941 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7000 Series

Section 14 Serial Communication Interface (SCI)
Clock
Either an internal clock generated by the built-in baud rate generator or an external clock input at
the SCK pin can be selected as the SCI’s serial clock, according to the setting of the C/A bit in
SCSMR and the CKE1 and CKE0 bits in SCSCR. For details of SCI clock source selection, see
table 14.9.
When an external clock is input at the SCK pin, the clock frequency should be 16, 8, or 4 times the
bit rate used.
When the SCI is operated on an internal clock, the clock can be output from the SCK pin. The
frequency of the clock output in this case is 16, 8, or 4 times the bit rate.
Data Transmit/Receive Operations
SCI Initialization (Asynchronous Mode): Before transmitting and receiving data, it is necessary
to clear the TE and RE bits to 0 in SCSCR, then initialize the SCI as described below.
When the operating mode, communication format, etc., is changed, the TE and RE bits must be
cleared to 0 before making the change using the following procedure. When the TE bit is cleared
to 0, the transmit shift register (SCTSR) is initialized. Note that clearing the TE and RE bits to 0
does not change the contents of the serial status 1 register (SC1SSR), the transmit FIFO data
register (SCFTDR), or the receive FIFO data register (SCFRDR). The TE bit should not be cleared
to 0 until all transmit data has been transmitted and the TEND flag has been set in SC1SSR. It is
possible to clear the TE bit to 0 during transmission, but the data being transmitted will go to the
high-impedance state after TE is cleared. Also, before starting transmission by setting TE again,
the TFRST bit should first be set to 1 in SCFCR to reset SCFTDR.
When an external clock is used the clock should not be stopped during operation, including
initialization, since operation will be unreliable in this case.
Figure 14.4 shows a sample SCI initialization flowchart.
Rev. 5.00 Sep 11, 2006 page 560 of 916
REJ09B0332-0500