HD64F36024FX Datasheet, PDF (191/386 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

Section 11 Timer W
11.5.8 Timing of Status Flag Clearing
When the CPU reads a status flag while it is set to 1, then writes 0 in the status flag, the status flag
is cleared. Figure 11.23 shows the status flag clearing timing.
φ
Address
Write signal
TSRW write cycle
T1 T2
TSRW address
IMFA to IMFD
IRRTW
Figure 11.23 Timing of Status Flag Clearing by CPU
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.
Rev. 4.00 Sep. 23, 2005 Page 163 of 354
REJ09B0025-0400