Using Interval Timer Mode; Notes On Board Design - Hitachi SH7750 series Hardware Manual

10.9.4

Using Interval Timer Mode

When the WDT is operating in interval timer mode, an interval timer interrupt is generated each
time the counter overflows. This enables interrupts to be generated at fixed intervals.
1. Clear the WT/,7 bit in the WTCSR register to 0, select the count clock with bits CKS2–CKS0,
and set the initial value in the WTCNT counter.
2. When the TME bit in the WTCSR register is set to 1, the count starts in interval timer mode.
3. When the counter overflows, the WDT sets the IOVF flag in the WTCSR register to 1, and
sends an interval timer interrupt request to INTC. The counter continues counting.
10.10

Notes on Board Design

When Using a Crystal Resonator: Place the crystal resonator and capacitors close to the EXTAL
and XTAL pins. To prevent induction from interfering with correct oscillation, ensure that no
other signal lines cross the signal lines for these pins.
Avoid crossing signal lines
Note: The values for CL1, CL2, and the damping resistance should be determined after
consultation with the crystal resonator manufacturer.
Figure 10.4 Points for Attention when Using Crystal Resonator
When Inputting External Clock from EXTAL Pin: Make no connection to the XTAL pin.
Rev. 4.0, 04/00, page 214 of 850
CL1 CL2
R
EXTAL XTAL
SH7750 Series
Recommended values
CL1 = CL2 = 0–33 pF
R = 0Ω