NEC mPD789101, User Manual

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CHAPTER 9 8-BIT TIMER/EVENT COUNTER
User’s Manual U13045EJ2V0UM00
127
9.5 Notes on Using 8-Bit Timer/Event Counter
(1) Error on starting timer
An error of up to 1 clock occurs after the timer has been started until a coincidence signal is generated. This
is because 8-bit timer register 80 (TM80) is started in asynchronization with the count pulse.
Figure 9-8. Start Timing of 8-Bit Timer Register
(2) Setting of 8-bit compare register 80
8-bit compare register 80 (CR80) can be set to 00H.
Therefore, one pulse can be counted when the 8-bit timer/event counter operates as an event counter.
Figure 9-9. External Event Counter Operation Timing
Cautions 1. When rewriting CR80 in timer counter operation mode (i.e. PWME80 (bit 6 of 8-bit timer
mode control register 80 (TMC80) is set to 0), be sure to stop the timer operation before
hand. If CR80 is rewritten in the timer operation-enabled state, a match interrupt request
signal may occur at the moment of rewrite.
2. When rewriting CR80 in PWM output operation mode (PWME80 = 1), incorrect pulses may
occur. Therefore, be sure to stop the timer operation when rewriting.
3. Do not set CR80 to 00H in the PWM output mode (when PWME80 = 1: bit 6 of 8-bit timer
mode control register 80 (TMC80)); otherwise, PWM may not be output normally.
Count pulse
TM80
count value
Timer start
00H 01H 02H 03H 04H
Tl80 input
CR80 00H
TM80
count value
00H 00H 00H 00H
Interrupt request flag