Switching Of Internal Clocks And Tcnt Operation - Hitachi H8S/2378, H8S/2378R Series Hardware Manual

13.8.5

Switching of Internal Clocks and TCNT Operation

TCNT may increment erroneously when the internal clock is switched over. Table 13.5 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 13.5, 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.
Rev. 1.0, 09/01, page 609 of 904