Application Notes - Renesas H8 Series Hardware Manual

9.5.5

Application Notes

Internal Clock Switching and TCG Operation
Depending on the timing, TCG may be incremented by a switch between different internal clock
sources. Table 9.13 shows the relation between internal clock switchover timing (by write to bits
CKS1 and CKS0) and TCG operation.
When TCG is internally clocked, an increment pulse is generated on detection of the falling edge
of an internal clock signal, which is divided from the system clock (φ) or subclock (φw). For this
reason, in a case like No. 3 in table 9.13 where the switch is from a high clock signal to a low
clock signal, the switchover is seen as a falling edge, causing TCG to increment.
Table 9.13 Internal Clock Switching and TCG Operation
Clock Levels Before and After
No. Modifying Bits CKS1 and CKS0
1 Goes from low level to low level
2 Goes from low level to high level
TCG Operation
Clock before
switching
Clock after
switching
Count
clock
TCG N
Write to CKS1 and CKS0
Clock before
switching
Clock after
switching
Count
clock
TCG N
Rev. 7.00 Mar 10, 2005 page 295 of 652
Section 9 Timers
N+1
N+1 N+2
Write to CKS1 and CKS0
REJ09B0042-0700