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9. Switching SCK
function
3
If pin SCK
is used as a clock output pin by SCI3 in synchronous mode and is then switched to a
3
general input/output pin (a pin with a different function), the pin outputs a low level signal for half
a system clock (ø) cycle immediately after it is switched.
This can be prevented by either of the following methods according to the situation.
a. When an SCK
function is switched from clock output to non clock-output
3
When stopping data transfer, issue one instruction to clear bits TE and RE to 0 and to set bits
CKE1 and CKE0 in SCR3 to 1 and 0, respectively. In this case, bit COM in SMR should be left 1.
The above prevents SCK
from being used as a general input/output pin. To avoid an intermediate
3
level of voltage from being applied to SCK
, the line connected to SCK
should be pulled up to
3
3
the V
level via a resistor, or supplied with output from an external device.
CC
b. When an SCK
function is switched from clock output to general input/output
3
When stopping data transfer,
(i) Issue one instruction to clear bits TE and RE to 0 and to set bits CKE1 and CKE0 in SCR3 to
1 and 0, respectively.
(ii) Clear bit COM in SMR to 0
(iii) Clear bits CKE1 and CKE0 in SCR3 to 0
Note that special care is also needed here to avoid an intermediate level of voltage from being
applied to SCK
.
3
10. Set up at subactive or subsleep mode
At subactive or subsleep mode, SCI3 becomes possible use only at CPU clock is øw/2.
303
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