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Rev. 1.00, 05/04, page 253 of 544
12.4.4 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 shown in figure 12.5. 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 in SSR is set to 1. Note that clearing
the RE bit to 0 does not initialize the contents of the RDRF, PER, FER, and ORER flags in SSR,
or the contents of RDR. When an external clock is used in asynchronous mode, the clock must be
supplied even during initialization.
Wait
<Initialization completion>
Start initialization
Set data transfer/receive format in
SMR and SCMR
[1]
Set CKE1 and CKE0 bits in SCR
(TE and RE bits are 0)
No
Yes
Set value in BRR
Clear TE and RE bits in SCR to 0
[2]
[3]
Set TE and RE bits in
SCR to 1, and set RIE, TIE, TEIE,
and MPIE bits
[4]
1-bit interval elapsed?
[1] Set the clock selection in SCR.
Be sure to clear bits RIE, TIE,
TEIE, and MPIE, and bits TE and
RE, to 0.
When the clock is selected in
asynchronous mode, it is output
immediately after SCR settings are
made.
[2] Set the data transfer/receive format
in SMR and SCMR.
[3] Write a value corresponding to the
bit rate to BRR. Not necessary if
an external clock is used.
[4] Wait at least one bit interval, then
set the TE bit or RE bit in SCR to 1.
Also set the RIE, TIE, TEIE, and
MPIE bits.
Setting the TE and RE bits enables
the TxD and RxD pins to be used.
Figure 12.5 Sample SCI Initialization Flowchart