Hitachi H8S/2633 Hardware Manual page 638

Clock: Either an internal clock generated by the on-chip 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

When an external clock is input at the SCK pin, the clock frequency should be 16 times the bit rate

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 in the middle of the transmit data, as shown in figure 16-3.

Figure 16-3 Relation between Output Clock and Transfer Data Phase

Data Transfer Operations:

• SCI initialization (asynchronous mode)

Before transmitting and receiving data, you should 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.

(Asynchronous Mode)