11.9.6
Mode Setting with Cascaded Connection
If 16-bit count mode and compare-match count mode are set simultaneously, the input clock
pulses for TCNT0 and TCNT1 (or TCNTY and TCNTX) are not generated, and thus the counters
will stop operating. Simultaneous setting of these two modes should therefore be avoided.
Rev. 1.00, 09/03, page 297 of 704