HD6412320 RENESAS [Renesas Technology Corp], HD6412320 Datasheet - Page 660

• Manufacturer Part Number: HD6412320
• Description: Renesas 16-Bit Single-Chip Microcomputer H8S Family H8S-2300 Series
• Manufacturer: RENESAS [Renesas Technology Corp]

Section 14 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
14.9.
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 14.3.
0
D0
D1
D2
D3
D4
D5
D6
D7
0/1
1
1
1 frame
Figure 14.3 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.6.00 Sep. 27, 2007 Page 630 of 1268
REJ09B0220-0600