Hitachi H8/3048 Hardware Manual page 378

Example of Phase Counting Mode: Figure 10-44 shows an example of operations in phase
counting mode. Table 10-9 lists the up-counting and down-counting conditions for TCNT2.
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In phase counting mode both the rising and falling edges of TCLKA and TCLKB are counted.
The phase difference between TCLKA and TCLKB must be at least 1.5 states, the phase overlap
must also be at least 1.5 states, and the pulse width must be at least 2.5 states. See figure 10-45.
TCNT2 value
Counting up
TCLKB
TCLKA
Figure 10-44 Operation in Phase Counting Mode (Example)
Table 10-9 Up/Down Counting Conditions
Counting Direction Up-Counting
TCLKB
TCLKA Low
Phase
difference
TCLKA
TCLKB
Overlap
Figure 10-45 Phase Difference, Overlap, and Pulse Width in Phase Counting Mode
High Low
High
Phase
difference
Pulse width
Phase difference and overlap:
Pulse width:
Overlap
366
Counting down
Down-Counting
High Low
Low
Pulse width
at least 1.5 states
at least 2.5 states
Time
High