MC68HC908LJ24 Datasheet, PDF (228/464 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Real Time Clock (RTC)
The mechanism uses the RTCWE[1:0] bits in the RTC calibration control
register (RTCCOMR) in a state machine, which requires a bit-write
sequence to disable the write-protection. A block diagram of the state
machine is shown in Figure 12-5.
RESET
Write-Protect
DISABLED
Write any value
other than 10
to RTWE
Note: Reading RTCWE[1:0]
always return 00.
RTCWE = 00
Write any value
other than 00
to RTWE
Write-Protect ENABLED
Write _{10 to RTCWE}
Write ^{any value other than 10 to RTCWE}
RTCWE = 10
Write _{any value other than 11 to RTCWE}
RTCWE 01
Write ^{01 to RTCWE}
RTCWE = 11
Data Sheet
228
Figure 12-5. RTC Write Protect State Diagram
After a reset, the write-protect mechanism is disabled, allowing the user
code to calibrate the RTC clock, set the time in the clock registers, and
set the date in the calendar registers.
To enable write-protect after reset or write-protect is disabled execute
the following code:
RTCWE1 EQU 1
RTCWE0 EQU 0
;RTCWE1 bit
;RTCWE0 bit
MC68HC908LJ24/LK24 — Rev. 2
Real Time Clock (RTC)
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