Renesas Hitachi H8S/2191, Hardware Manual

Page: 415 / 1065

Rev. 2.0, 11/00, page 388 of 1037
17.7.4 Changing Over the Internal Clocks and Counter Operations
Depending on the timing of changing over the internal clocks, the FRC may count up. Table
17.6 indicated below shows the relations between the timing of changing over the internal clocks
(Re-writing of the CKS1 and CKS0) and the FRC operations.
When using an internal clock, the counting clock is being generated detecting the falling edge of
the internal clock dividing the system clock (
φ
). For this reason, like Item No. 3 of table 17.6,
count clock signals are issued deeming the timing before the changeover as the falling edge to
have the FRC to count up.
Also, when changing over between an internal clock and the external clock, the FRC may count
up.
Table 17.6 Changing Over the Internal Clocks and the FRC Operation
No.
Re-writing timing
for the CKS1 and
CKS0
FRC operation
1 Low
→
Low level
changeover
Clock before
the changeover
Clock after
the changeover
Count
clock
FRC
Re-writing of the CKS1 and CKS0
N N+1
2 Low
→
High level
changeover
Clock before
the changeover
Clock after
the changeover
Count
clock
FRC
Re-writing of the CKS1 and CKS0
N N+1 N+2