9.
Switching SCK
3
function
If pin SCK
3
is used as a clock output pin by SCI3 in synchronous mode and is then switched to a
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
3
function is switched from clock output to non clock-output
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
3
from being used as a general input/output pin. To avoid an intermediate level
of voltage from being applied to SCK
3
, the line connected to SCK
3
should be pulled up to the V
CC
level via a resistor, or supplied with output from an external device.
b.
When an SCK
3
function is switched from clock output to general input/output
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.
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