66 the divider control bits can select the operating
mode, or be used to hold the divider chain reset
which allows precision setting of the time. When
the divider chain is changed from reset to the
operating mode, the first update cycle is one-half
second later. The divider control bits are also used
to facilitate testing of the RTC.
Periodic Interrupt Selection
The periodic interrupt allows the IRQB port to be
triggered from once every 500 ms to once every
122.07 μs. As Table 67 shows, the periodic
interrupt is selected with the RS0-RS3 bits in
Register A. The periodic interrupt is enabled with
the PIE bit in Register B.
147