Usually, a beeper doesn't oscillate by itself, it has an external circuit to automatically turn it high/low(like a 555 timer, or XTAL+divider), and then another (software controlled) line to enable/disable it.
*edit* top-left corner looks like a small XTAL, probably 32768Hz? for IRQ and beeper.

BTW that CPU is 1MHz, I guess it implies that the 1st Mondial is 1MHz, 2nd version is 2MHz.