Reset
(Locked)
K0
(Locked)
K1
(Unlocked)
KICK0 = Any Value
or
KICK1 ≠ Key1
KICK0 = Key0
KICK1 = Key1
KICK0 = Key0
Reset
KICK1 = Any Value
or
KICK0 ≠ Key0
or
Reset
Key0
Key1
Locked
Unlocked
= 83E7 0B13h
= 95A4 F1E0h
= Write protection enabled
= Write protection disabled
KICK1 = Any Value
or
KICK0 ≠ Key0
or
Reset
Architecture
1325
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Real-Time Clock (RTC)
27.2.5.2 Periodic Interrupt Enable and Status Bits
The TIMER bit and EVERY field in the interrupt register (INTERRUPT) work together to enable periodic
interrupts. When the TIMER bit is enabled, interrupts are issued at a time period indicated by the EVERY
field (0 = Second, 1h = Minute, 2h = Hour, 3h = Day). Regardless of the period selected in the EVERY
field, the periodic timer status bits (DAYEVT, HREVT, MINEVT, SECEVT) are set in the status register
(STATUS) whenever they are valid. Note that the appropriate status bits are set when the TIME bit is
enabled, not when the desired interrupt is generated. Active periodic status bits remain high as long as the
TIMER bit is enabled.
For example, if daily periodic interrupts are enabled and the time (in HH:MM:SS format) transitions from
23:59:59 to 00:00:00, the STATUS register sets all four periodic status bits (DAYEVT, HREVT, MINEVT,
and SECEVT) because all four time periods were incremented. These bits all remain high until:
1. The TIME bit is cleared and all four status bits clear to zero until TIME is set again
OR
2. The current time reaches 00:00:01. At that point, the SECEVT remains set while the DAYEVT,
HREVT, and MINEVT bits are cleared. The next interrupt is not generated until the next day transition.
As with writing to time and calendar registers (
), writes to the INTERRUPT and STATUS
registers should only be done when the RTC is stopped or when the BUSY bit is low.
Note that all registers in the RTC except for KICK
n
R have write-protection. See
for
information on unlocking registers.
27.2.6 Register Protection Against Spurious Writes
All registers in the RTC except for the KICK
n
R registers are protected from spurious writes. Out of reset,
writes to protected registers are disabled until the registers are unlocked using the KICK
n
R registers. To
unlock the registers, a key of 83E7 0B13h needs to be written to KICK0R, followed by a write of
95A4 F1E0h to KICK1R. Registers remain unlocked until write protection is enabled again by writing any
value to KICK0R or KICK1R. The write protection state machine is shown in
.
Figure 27-3. Kick State Machine