On the 84+, ports 41 through 44 (LSB to MSB) are used to set the clock with the number of seconds since January 1, 1997 12:00 AM. After outputting the values, you must output 01h to port 40 followed by 03h to port 40 in order to set the clock.

Bit 0 of port 40 controls whether the clock is active.

The current value of the clock is stored in ports 45-48 (from LSB to MSB accordingly) as seconds since January 1, 1997 12:00 AM.