URTC-8 Universal RTC for Z80 computers
About uRTC-8
uRTC-8 is a universal RTC that can be connected via a Z80 shim to any Z80 computer that has a socketed CPU. It uses an 8 bit comparator and a set of jumpers to enable I/O base address selection, just like uIDE-8. The RTC used is an Epson RTC72421 which has 16 registers, directly accessible via IN and OUT instructions. As a result, the base I/O address is a four bit number between 0000 and 1111 (0-15), putting the device at any of the I/O addresses 00h, 10h, 20h, 30h, 40h, 50h, 60h, 70h, 80h, 90h, A0h, B0h, C0h, D0h, E0h or F0h. From that address to xFh are the 16 registers of the Epson RTC.
uRTC is powered by the host computer, but also has a battery backed supply to maintain the time and date when the host is powered down. The battery is a common CR2032 3v button cell.
Along with the device itself, there are two downloadable utilities:
- uRTC.COM allows the user to set and get the time on the RTC chip.
- uRTCTX.com transfers the time and date to the host computer's operating system (normally CP/M).
Project status
As of this time (April 2019), the uRTC boards are designed and in fabrication. Work has started on the utilities.
Technical info
This is the technical application manual for the 72421 RTC chip used in uRTC-8.
