HD64F2357VF13 Datasheet, PDF (481/1049 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

12.6.5 Switching of Internal Clocks and TCNT Operation
TCNT may increment erroneously when the internal clock is switched over. Table 12-5 shows the relationship between
the timing at which the internal clock is switched (by writing to the CKS1 and CKS0 bits) and the TCNT operation.
When the TCNT clock is generated from an internal clock, the falling edge of the internal clock pulse is detected. If clock
switching causes a change from high to low level, as shown in case 3 in table 12-5, a TCNT clock pulse is generated on
the assumption that the switchover is a falling edge. This increments TCNT.
The erroneous incrementation can also happen when switching between internal and external clocks.
Table 12-5 Switching of Internal Clock and TCNT Operation
Timing of Switchover
by Means of CKS1
No.
and CKS0 Bits
TCNT Clock Operation
1
Switching from
low to low*¹
Clock before
switchover
Clock after
switchover
TCNT clock
2
Switching from
low to high*²
TCNT
Clock before
switchover
Clock after
switchover
TCNT clock
N
N+1
CKS bit write
TCNT
N
3
Switching from
high to low*³
Clock before
switchover
Clock after
switchover
TCNT clock
N+1
N+2
CKS bit write
*⁴
TCNT
N
N+1
N+2
CKS bit write
Rev.6.00 Oct.28.2004 page 451 of 1016
REJ09B0138-0600H