On the Sharp PC-E220 is a fixed timer signal availible, named 1S.

It is the clock signal for the LCD drivers and has a slightly period variation
between 0.92 and 0.98 sec.
This signal is switching every 468 - 487 msec interval between 0 and 1
whereas the period length is increasing slowly with raising temperature.

The corresponding interrupt from this signal can be enabled/disabled by
Bit 2 of port 17H.
And the interrupt status (pending or not) can be asked from
Bit 2 of port 16H.
Also this bit on port 16H must be set to 1 to clear a pending signal!

There exists a mechanism to half the period by writing on port 14H.