Hitachi H8/3035 Series Hardware Manual page 237

 Buffer transfer at transition from down-counting to up-counting
If the general register value is in the range from H'0000 to T – 1, do not transfer a buffer
register value outside this range. Conversely, when a general register value is outside this
range, do not transfer a value within this range. See figure 8-41.
GRA3
GR
H'0000
Output pin
Output pin
BR
GR
Write during down-counting
Figure 8-41 Changing a General Register Setting by Buffer Transfer (Caution 2)
 General register settings outside the counting range (H'0000 to GRA3)
Waveforms with a duty cycle of 0% or 100% can be output by setting a general register
to a value outside the counting range. When a buffer register is set to a value outside the
counting range, then later restored to a value within the counting range, the counting
direction (up or down) must be the same both times. See figure 8-42.
0% duty cycle 100% duty cycle
Write during up-counting
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