SH7727 Datasheet, PDF (585/1109 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7700 Series

Section 17 Serial Communication Interface (SCI)
Clock
An internal clock generated by the on-chip baud rate generator or an external clock input from the
SCK0 pin can be selected as the SCI transmit/receive clock. The clock source is selected by the
C/A bit in the serial mode register (SCSMR) and bits CKE1 and CKE0 in the serial control
register (SCSCR) (table 17.10).
When an external clock is input at the SCK0 pin, it must have a frequency equal to 16 times the
desired bit rate.
When the SCI operates on an internal clock, it can output a clock signal at the SCK0 pin. The
frequency of this output clock is equal to the bit rate. The phase is aligned as in figure 17.6 so that
the rising edge of the clock occurs at the center of each transmit data bit.
0 D0 D1 D2 D3 D4 D5 D6 D7 0/1 1 1
1 frame
Figure 17.6 Relationship between Output Clock and Transfer Data Phase
(Asynchronous Mode)
Transmitting and Receiving Data
SCI Initialization (Asynchronous Mode):
Before transmitting or receiving, clear the TE and RE bits to 0 in the serial control register
(SCSCR), then initialize the SCI as follows.
When changing the operation mode or communication format, always clear the TE and RE bits to
0 before following the procedure given below. Clearing TE to 0 sets TDRE to 1 and initializes the
transmit shift register (SCTSR). Clearing RE to 0, however, does not initialize the RDRF, PER,
FER, and ORER flags or receive data register (SCRDR), which retain their previous contents.
When an external clock is used, the clock should not be stopped during initialization or subsequent
operation. SCI operation becomes unreliable if the clock is stopped.
Figure 17.7 is a sample flowchart for initializing the SCI. The procedure for initializing the SCI is:
Rev. 5.00 Dec 12, 2005 page 513 of 1034
REJ09B0254-0500