HD64F2149 Datasheet, PDF (475/1035 Pages) Renesas Technology Corp – Hitachi 16-Bit Single-Chip Microcomputer

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 15.9.
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 15.3.
0 D0 D1 D2 D3 D4 D5 D6 D7 0/1 1 1
1 frame
Figure 15.3 Relation between Output Clock and Transfer Data Phase
(Asynchronous Mode)
Data Transfer Operations
SCI Initialization (Asynchronous Mode): Before transmitting and 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 is uncertain.
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