Figure 1 -- RTC Interface Block Diagram
        
        
                                  /-----------\
                                  | MC146818  |
                                  | RTC + RAM |
                                  \-----------/
                                    |   |   |
                      /-------------/   |   \-------------\
                      |                 |                 |
                 /---------\       /---------\       /---------\
                 | INT 70H |       | INT 1AH |       | INT 15H |
                 | RTC ISR |       |   TIME  |       |   WAIT  |
                 \---------/       \---------/       \---------/
                   |  |                 |                 |
                   |  \--------------\  |  /--------------/
                   |                 |  |  |
              /---------\          /---------\
              | INT 4AH |          |   BIOS  |
              |  ALARM  |          |   DATA  |
              \---------/          \---------/