R01UH0823EJ0100 Rev.1.00
Page 751 of 1823
Jul 31, 2019
RX23W Group
26. 8-Bit Timer (TMR)
26.8.6
Conflict 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 methods high for compare match A and compare match B, as listed in
26.8.7
Switching of Internal Clocks and TCNT Operation
TCNT may be incremented erroneously depending on when the internal clock is switched.
lists the
relationship between the timing at which the internal clock is switched (by writing to the TCCR.CKS[2:0] bits) and the
operation of TCNT.
When TCNT count clock is generated from an internal clock, the rising edge of the internal clock pulse are always
monitored. If the signal levels of the clocks before and after switching change from low to high as shown in No. 2 in
, the change is considered as an edge. Therefore, a TCNT count clock is generated and TCNT is incremented.
The erroneous increment of TCNT can also happen when switching between internal and internal clocks.
Table 26.7
Timer Output Priorities
Output Setting
Priority
Toggle output
High
Low
High output
Low output
No change
Table 26.8
Switching of Internal Clocks and TCNT Operation (1/2)
No.
Timing to Change the
TCCR.CKS[2:0] Bits
TCNT Counter Operation
1
Switching from low to low*
2
Switching from low to high*
Clock before
switching
Clock after
switching
TCNT count
clock
TCNT
TCCR.CKS[2:0] bits changed
N + 1
N
N + 2
Clock before
switching
Clock after
switching
TCNT count
clock
TCNT
TCCR.CKS[2:0] bits changed
*3
N + 1
N
N + 2
N + 3
