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16.8.6
SCI Operations during Mode Transitions
Transmission: Before making the transition to module stop, software standby, or subsleep mode,
stop all operations (TE = TIE = TEIE = 0). TSR, TDR, and SSR are reset. The states of the
output pins during each mode depend on the port settings, and the pins output a high-level signal
after mode cancellation. If the transition is made during data transmission, the data being
transmitted will be undefined.
To transmit data in the same transmission mode after mode cancellation, set the TE bit to 1, read
SSR, write to TDR, clear TDRE to 0 in this order, and then start transmission. To transmit data in
a different transmission mode, initialize the SCI first.
Figure 16.21 shows a sample flowchart for mode transition during transmission. Figures 16.22
and 16.23 show the pin states during transmission.
<Transmission>
All data transmitted?
Read TEND flag in SSR
Make transition to software standby mode etc.
Cancel software standby mode etc.
Change operating mode?
<Start transmission>
Figure 16.21 Sample Flowchart for Mode Transition during Transmission
Rev. 1.00, 09/03, page 470 of 704
No
Yes
No
TEND = 1
Yes
TE = 0
[2]
No
Yes
Initialization
[1]
[1] Data being transmitted is lost
halfway. Data can be normally
transmitted from the CPU by
setting TE to 1, reading SSR,
writing to TDR, and clearing
TDRE to 0 after mode
cancellation; however, if the DTC
has been initiated, the data
remaining in DTC RAM will be
transmitted when TE and TIE are
set to 1.
[2] Clear TIE and TEIE to 0 when
they are set to 1.
[3]
[3] Module stop mode is included.
TE = 1
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