Contention Between Compare Matches A And B; Switching Of Internal Clocks And Tcnt Operation; Table 11.4 Timer Output Priorities - Hitachi H8S/2215 Series Hardware Manual

11.8.4

Contention between Compare Matches A and B

If compare match events A and B occur at the same time, the 8-bit timer operates in accordance
with the priorities for the output statuses set for compare match A and compare match B, as shown
in table 11.4.

Table 11.4 Timer Output Priorities

Output Setting
Toggle output
1 output
0 output
No change
11.8.5

Switching of Internal Clocks and TCNT Operation

TCNT may increment erroneously when the internal clock is switched over. Table 11.5 shows the
relationship between the timing at which the internal clock is switched (by writing to the CKS1
and CKS0 bits) and the TCNT operation.
When the TCNT clock is generated from an internal clock, the falling edge of the internal clock
pulse is detected. If clock switching causes a change from high to low level, as shown in case 3 in
table 11.5, a TCNT clock pulse is generated on the assumption that the switchover is a falling
edge. This increments TCNT.
The erroneous incrementation can also happen when switching between internal and external
clocks.
Rev. 3.0, 10/02, page 344 of 686
Priority
High
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