This is the technical application manual for the 72421 RTC chip used in uRTC-8. Of particular interest are the registers.
RTCBASE .equ 0A0h ; Default uRTC base I/O address rtc1sec .db RTCBASE+00h ; 1 second digit
rtc10sec .db RTCBASE+01h ; 10 second digit
rtc1min .db RTCBASE+02h ; 1 minute digit
rtc10min .db RTCBASE+03h ; 10 minute digit
rtc1hour .db RTCBASE+04h ; 1 hour digit
rtc10hour .db RTCBASE+05h ; 10 hour digit (also AM/PM indicator)
rtc1day .db RTCBASE+06h ; 1 day digit
rtc10day .db RTCBASE+07h ; 10 day digit
rtc1month .db RTCBASE+08h ; 1 month digit
rtc1year .db RTCBASE+0Ah ; 1 year digit
rtc10year .db RTCBASE+0Bh ; 10 year digit
rtcweek .db RTCBASE+0Ch ; day of week
rtccrtlD .db RTCBASE+0Dh ; control register D
rtcctrlE .db RTCBASE+0Eh ; control register E