HD6433640 HITACHI [Hitachi Semiconductor], HD6433640 Datasheet - Page 279

• Manufacturer Part Number: HD6433640
• Description: H8/3644 Series Hardware Manual
• Manufacturer: HITACHI [Hitachi Semiconductor]

4. Internal clock switching and counter operation
Table 9.19 Internal Clock Switching and FRC Operation
No.
1
2
Depending on the timing, FRC may be incremented by a switch between different internal
clock sources. Table 9.19 shows the relation between internal clock switchover timing (by
writing to bits CKS1 and CKS0) and FRC operation.
When FRC is internally clocked, an increment pulse is generated from the falling edge of an
internal clock signal, which is divided from the system clock (ø). For this reason, in a case like
No. 3 in table 9.19 where the switch is from a high clock signal to a low clock signal, the
switchover is seen as a falling edge, causing FRC to increment.
FRC can also be incremented by a switch between internal and external clocks.
Clock Levels Before
and After Modifying
Bits CKS1 and CKS0
Goes from low level
to low level
Goes from low
to high
FRC Operation
Clock before
switching
Clock after
switching
Count clock
FRC
Clock before
switching
Clock after
switching
Count clock
FRC
Write to CKS1 and CKS0
N
N
N + 1
Write to CKS1 and CKS0
N + 1
N + 2
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