Hitachi H8S/2338 Series Hardware Manual page 428

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 11-9.
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 11-3.
0 D0
Figure 11-3 Relation between Output Clock and Transfer Data Phase
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.
D1 D2 D3 D4
1 frame
(Asynchronous Mode)
D5 D6 D7 0/1 1 1
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