Cautions For 16-Bit Timer/Event Counter 00 - NEC 78K0 User Manual

6.5 Cautions for 16-Bit Timer/Event Counter 00

(1) Timer start errors
An error of up to one clock may occur in the time required for a match signal to be generated after timer start.
This is because 16-bit timer counter 00 (TM00) is started asynchronously to the count clock.
Count clock
TM00 count value
(2) 16-bit timer capture/compare register setting (in the mode in which clear & start occurs on match
between TM00 and CR000)
Set 16-bit timer capture/compare registers 000 and 010 (CR000 and CR010) to other than 0000H. This means a
1-pulse count operation cannot be performed when 16-bit timer/event counter 00 is used as an event counter.
(3) Capture register data retention
The values of 16-bit timer capture/compare registers 000 and 010 (CR000 and CR010) are not guaranteed after
16-bit timer/event counter 00 has been stopped.
(4) Valid edge setting
Set the valid edge of the TI000 pin after setting bits 2 and 3 (TMC002 and TMC003) of 16-bit timer mode control
register 00 (TMC00) to 0, 0, respectively, and then stopping timer operation. The valid edge is set using bits 4
and 5 (ES000 and ES001) of prescaler mode register 00 (PRM00).
(5) Re-triggering one-shot pulse
(a) One-shot pulse output by software
When a one-shot pulse is output, do not set the OSPT00 bit to 1. Do not output the one-shot pulse again
until INTTM000, which occurs upon a match with the CR000 register, or INTTM010, which occurs upon a
match with the CR010 register, occurs.
(b) One-shot pulse output with external trigger
If the external trigger occurs again while a one-shot pulse is output, it is ignored.
(c) One-shot pulse output function
When using the one-shot pulse output of 16-bit timer/event counter 00 with a software trigger, do not change
the level of the TI000 pin or its alternate-function port pin.
Because the external trigger is valid even in this case, the timer is cleared and started even at the level of the
TI000 pin or its alternate-function port pin, resulting in the output of a pulse at an undesired timing.
CHAPTER 6 16-BIT TIMER/EVENT COUNTER 00
Figure 6-35. Start Timing of 16-Bit Timer Counter 00 (TM00)
0000H
Timer start
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0001H 0002H 0003H 0004H
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