Rev. 1.0, 02/00, page 426 of 1141
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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/
$
bit
in SMR1 and the CKE1 and CKE0 bits in SCR1. For details of SCI clock source selection, see
table 22.9.
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 22.3.
0
1 frame
D0
D1
D2
D3
D4
D5
D6
D7
0/1
1
1
Figure 22.3 Relation between Output Clock and Transfer Data Phase
(Asynchronous Mode)