Operation; Tcnt Incrementation Timing - Hitachi H8/329 Series Hardware Manual

7.3 Operation

7.3.1 TCNT Incrementation Timing

The timer counter increments on a pulse generated once for each period of the selected (internal or
external) clock source.
Internal Clock: Internal clock sources are created from the system clock by a prescaler.
Thecounter increments on an internal TCNT clock pulse generated from the falling edge of the
prescaler output, as shown in figure 7-2. Bits CKS2 to CKS0 of the TCR and bits ICKS1 and
ICKS0 of the STCR can select one of the six internal clocks.
Ø
Internal
clock
TCNT clock
pulse
TCNT N–1
Figure 7-2. Count Timing for Internal Clock Input
External Clock: If external clock input (TMCI) is selected, the timer counter can increment on the
rising edge, the falling edge, or both edges of the external clock signal. Figure 7-3 shows
incrementation on both edges of the external clock signal.
The external clock pulse width must be at least 1.5 system clock periods for incrementation on a
single edge, and at least 2.5 system clock periods for incrementation on both edges. See
figure 7-4. The counter will not increment correctly if the pulse width is shorter than these values.
N
152
N+1