4-bit real-time clock (RTC)

This is the RTC 72421 board for the I/O bus (see the specs for the reZet80 I/O bus).

The RTC-72421 is a 4-bit real-time clock with a parallel interface.
It provides 16 registers that store time (hour, minute, second) and calendar (year, month, day, day of the week).
Battery backup, automatic leap year correction and a fixed-period interrupt are also included.

Bill of materials:
- PCB 5x7 cm (at least 22 rows)
- 22-pin right-angled male connector
- DIP-18 narrow socket
- RTC-72421
- CR2032 3V battery
- battery holder
- 2x schotthy diode IN5817
- capacitor 100 nF
- capacitor 47 uF