This device is a virtualization of the RTC portion of Norberto Collado's H89 SBC RTC Speed Parallel modern add-on to H89 computers. It provides a real time clock/calendar chip with battery backup. It is used by CP/M 3 to get the current time/date at boot time, and if the user sets time/date it is stored to the chip.
The device uses the default port of 0A0H (240Q), as indicated in schematics. Software is hard-coded to that port.
This virtualization provides an interface to the host computer's clock. Since the chip uses 2-digit years, all years are assumed to be in the 21st century (years 2000-2099). If the user sets the time/date, the virtual RTC computes the difference and uses that for future time acquisition, until time is set again or the simulation ends. The simulation always begins with the host computer clock synchronized to the virtual RTC.
There is also an RTC board for the H8, which uses the same RTC chip but provides different additional features. This H8 board specifies the same default port as the H89 variant (the CP/M 3 RTC module should work for both).