Cautions - NEC V850/SA1 mPD703015 Preliminary User's Manual

7.4.5 Cautions

(1) Error when the timer starts
The time until the coincidence signal is generated after the timer starts has a maximum error of one clock. The
reason is the starting of the 8-bit counter n (TMn) is asynchronous with respect to the count pulse.
Count pulse
TMn count value
Remark n = 2 to 5
(2) Operation after the compare register is changed while the timer is counting
If the value after the 8-bit compare register n (CRn0) changes is less than the value of the 8-bit timer register
(TMn), counting continues, overflows, and counting starts again from 0. Consequently, when the value (M) after
CRn0 changes is less than the value (N) before the change, the timer must restart after CRn0 changes.
Figure 7-44. Timing After Compare Register Changes During Timer Counting
Count pulse
CRn0
TMn count value
Remarks 1. N > X > M
2. n = 2 to 5
Caution Except when the TIn input is selected, always set TCEn = 0 before setting the stop state.
(3) TMn read out during timer operation
Since reading out TMn during operation occurs while the selected clock is temporarily stopped, select some high
or low level waveform that is longer than the selected clock.
194
CHAPTER 7 TIMER/COUNTER FUNCTION
Figure 7-43. Start Timing of Timer n
00H 01H
↑
Timer starts
N
X-1 X
02H
03H 04H
M
FFH
00H
01H
02H