Datasheet

Real Time Clock (RTC)
RTC Register and Bit Write Protection
MC68HC908LJ24/LK24 — Rev. 2.1 Data Sheet
Freescale Semiconductor Real Time Clock (RTC) 227
Figure 12-4. 1-Hz Clock Compensation
12.8 RTC Register and Bit Write Protection
A write-protect mechanism is implemented to prevent accidental writes
to the RTC clock registers, calendar registers, and other control bits. The
protected RTC registers and bits are listed in Table 12-3.
CGMXCLK
TRUE 15 SECONDS
COMPENSATED
1-Hz CLOCK
UNCOMPENSATED
1-Hz CLOCK
(CGMXCLK ÷ 32768)
PERIOD A PERIOD B
1-Hz CLOCK = CGMXCLK
÷ A 1-Hz CLOCK = CGMXCLK ÷ B
Table 12-3. Write-Protected RTC Registers and Bits
Register Bit
RTC Control Register 1
CAL
AUTOCAL
OUTF[1:0]
RTC Control Register 2
COMEN
RTCE
Second Register (All Bits)
Minute Register (All Bits)
Hour Register (All Bits)
Day-Of-Week Register (All Bits)
Day Register (All Bits)
Month Register (All Bits)
Year Register (All Bits)