192
9.4.5
Application Notes
Input Clock Switching and TCG Operation: Depending on when the input clock is switched,
there will be cases in which TCG is incremented in the process. Table 9.11 shows the relation
between internal clock switchover timing (selected in bits CKS1 and CKS0) and TCG operation.
If an internal clock (derived from the system clock ø or subclock ø
SUB
) is used, an increment pulse
is generated when a falling edge of the internal clock is detected. For this reason, in a case like No.
3 in table 9.11, where the clock is switched at a time such that the clock signal goes from high
level before switching to low level after switching, the switchover is seen as a falling edge to
generate the count clock, causing TCG to be incremented.
Table 9.11
Internal Clock Switching and TCG Operation
No.
Clock Levels Before
and After Modifying
Bits CKS1 and CKS0
TCG Operation
1
Goes from low level
to low level
N +1
Clock before
switching
Clock after
switching
Count clock
TCG
CKS bits modified
N
2
Goes from low level
to high level
N +1
N +2
Clock before
switching
Clock after
switching
Count clock
TCG
CKS bits modified
N