Epson S1C63616 Technical Manual page 127

(6) For the reason below, pay attention to the reload data write timing when changing the interval of the
programmable timer interrupts while the programmable timer is running.
The programmable timer counts down at the falling edge of the input clock and at the same time it gen-
erates an interrupt if the counter underflows. Then it starts loading the reload data to the counter and
the counter data is determined at the next rising edge of the input clock (period shown in as ➀ in the
figure).
Count clock
Counter data
(continuous mode)
To avoid improper reloading, do not rewrite the reload data after an interrupt occurs until the counter
data is determined including the reloading period ➀ . Be especially careful when using the OSC1 (low-
speed clock) as the clock source of the programmable timer and the CPU is operating with the OSC3
(high-speed clock).
(7) The programmable timer count clock does not synch with the CPU clock. Therefore, the correct value
may not be obtained depending on the count data read and count-up timings. To avoid this problem,
the programmable timer count data should be read by one of the procedures shown below.
• Read the count data twice and verify if there is any difference between them.
• Temporarily stop the programmable timer when the counter data is read to obtain proper data.
03H 02H 01H
Underflow (interrupt is generated)
Fig. 4.9.11.3 Reload timing for programmable timer
➀
00H 25H 24H
Counter data is determined by reloading.
SIC63616-(Rev. 1.0) NO. P120
(Reload data = 25H)
3240-0412