Rev. 1.0, 03/01, page 147 of 280
11.6
Usage Notes
The following types of contention or operation can occur in timer W operation.
1. The pulse width of the input clock signal and the input capture signal must be at least two
system clock(
φ
) cycles; shorter pulses will not be detected correctly.
2. Writing to registers is performed in the T2 state of a TCNT write cycle.
If counter clear signal occurs in the T2 state of a TCNT write cycle, clearing of the counter
takes priority and the write is not performed, as shown in figure 11-24. If counting-up is
generated in the TCNT write cycle to contend with the TCNT counting-up, writing takes
precedence.
3. Depending on the timing, TCNT may be incremented by a switch between different internal
clock sources. When TCNT is internally clocked, an increment pulse is generated from the
rising edge of an internal clock signal, that is divided system clock (
φ
). Therefore, as shown in
figure 11-25 the switch is from a low clock signal to a high clock signal, the switchover is seen
as a rising edge, causing TCNT to increment.
4.
If timer W enters module standby mode while an interrupt request is generated, the interrupt
request cannot be cleared. Before entering module standby mode, disable interrupt requests.
Counter clear
signal
Write signal
Address
φ
TCNT address
TCNT
TCNT write cycle
T1
T2
N
H'0000
Figure 11-24 Contention between TCNT Write and Clear
Summary of Contents for H8/3670F-ZTAT HD64F3670
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