NEC uPD78P078 - Manual (Page 247)

247
CHAPTER 9 8-BIT TIMER/EVENT COUNTERS 1 AND 2
(3) Operation after compare register change during timer count operation
If the values after the 8-bit compare registers 10 and 20 (CR10 and CR20) are changed are smaller than
those of 8-bit timer registers (TM1 and TM2), TM1 and TM2 continue counting, overflow and then restart
counting from 0. Thus, if the value (M) after CR10 and CR20 change is smaller than value (N) before the
change, it is necessary to restart the timer after changing CR10 and CR20.
Figure 9-15. Timing after Compare Register Change during Timer Count Operation
Remark N > X > M
Count Pulse
CR10, CR20
TM1, TM2 Count Value X – 1 X FFH 00H 01H 02H
M N