Switching Of Internal Clock And Frc Operation; Figure 11.20 Conflict Between Ocr Write And Compare-Match (When Automatic Addition Function Is Used) - Renesas H8S Series Hardware Manual

Section 11 16-Bit Free-Running Timer (FRT)
Figure 11.20 Conflict between OCR Write and Compare-Match
11.7.4

Switching of Internal Clock and FRC Operation

When the internal clock is changed, the changeover may source FRC to increment. This depends
on the time at which the clock is switched (bits CKS1 and CKS0 are rewritten), as shown in table
11.3.
When an internal clock is used, the FRC clock is generated on detection of the falling edge of the
internal clock scaled from the system clock (φ). If the clock is changed when the old source is high
and the new source is low, as in case no. 3 in table 11.3, the changeover is regarded as a falling
edge that triggers the FRC clock, and FRC is incremented. Switching between an internal clock
and external clock can also source FRC to increment.
Rev. 3.00 Jul. 14, 2005 Page 302 of 986
REJ09B0098-0300
φ
Address
Internal write signal
OCRAR (OCRAF)
Compare-match signal
FRC
OCR
Automatic addition is not performed
because compare-match signals are disabled.
(When Automatic Addition Function is Used)
OCRAR (OCRAF)
address
Old data New data
Disabled
N
N
N+1