D12320VF25V Datasheet, PDF (498/1146 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

Section 12 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
SMR and the CKE1 and CKE0 bits in SCR. For details of SCI clock source selection, see table
12.9.
When an external clock is input at the SCK pin, the clock frequency should be 16 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 equal to the bit rate, and the phase is such that the
rising edge of the clock is at the center of each transmit data bit, as shown in figure 12.3.
0 D0 D1 D2 D3 D4 D5 D6 D7 0/1 1 1
1 frame
Figure 12.3 Relation between Output Clock and Transfer Data Phase
(Asynchronous Mode)
Data Transfer Operations
SCI initialization (asynchronous mode): Before transmitting or receiving data, first clear the TE
and RE bits in SCR to 0, then initialize the SCI as described below.
When the operating mode, transfer 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
TDRE flag is set to 1 and TSR is initialized. Note that clearing the RE bit to 0 does not change the
contents of the RDRF, PER, FER, and ORER flags, or the contents of RDR.
When an external clock is used the clock should not be stopped during operation, including
initialization, since operation will be unreliable in this case.
Rev.7.00 Feb. 14, 2007 page 464 of 1108
REJ09B0089-0700