You access the internal clock/calendar with the SVC_REQ function with function code 7. I typically set up SVC_REQ function with a parameter block of six words (16-bit). The first two words are control parameters, the remaining four are data returned by the function. The first word contains a value of zero to read the clock or 1 to set it. The second word contains a value that determines the format of the returned data. I use a value of 81 hex, for BCD, with a 4-digit year.
The third word will contain the year.
The fourth word will contain the day of the month in the high byte and the month in the low byte.
The fifth word will contain the the minute in the high byte and the hour in the low byte.
The sixth word will contain the day of the week(1 -76) in the high byte and seconds in the low byte.
To extract the hour, AND the fifth word with 00FF and convert the result from BCD to integer.