MC68HC908LJ24 Datasheet, PDF (233/464 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Real Time Clock (RTC)
RTC Registers
12.10.2 RTC Calibration Data Register (RTCCDAT)
The RTC calibration data register (RTCCDAT) contains the RTC
calibration data.
Address: $0041
Read: EOVL
0
Write:
E5
E4
E3
E2
E1
E0
Reset: U
0
U
U
U
U
U
U
Figure 12-7. RTC Calibration Data Register (RTCCDAT)
EOVL — E Register Overflow
This read-only bit indicates that the time difference recorded between
CALIN and CGMXCLK after 15 seconds during the last automatic
calibration had exceeded 31 CGMXCLK cycles. Clear this flag by
writing to the E register after the CAL bit is set. Setting the AUTOCAL
bit will also clear this flag, but subsequent automatic calibration may
set this flag again.
1 = E register overflow detected during the last automatic
calibration
0 = No E register overflow detected during last automatic
calibration
E[5:0] — RTC Compensation Value (E register)
E[5:0] is a two’s complement number which indicates the number of
CGMXCLK cycles the RTC requires to compensate for a 15 second
duration. If the compensation exceeds the limit of ±31 CGMXCLK
cycles, the E[5:0] bits remain at the maximum value of –30 (%100010)
or +30 (%011110), and the EOVL flag will be set.
When compensation is enabled (COMEN = 1): If E is negative, an E
number of cycles will be subtracted from the 491520 CGMXCLK
cycles (32768 × 15).
When compensation is enabled (COMEN = 1): If E is positive, an E
number of cycles will be added to the 491520 CGMXCLK cycles
(32768 × 15).
E[5:0] is written by the RTC compensation circuit during automatic
calibration (AUTOCAL = 1). User can only write to E{5:0] when
AUTOCAL = 0 and CAL = 1. Reset has no effect on E[1:0] bits.
MC68HC908LJ24/LK24 — Rev. 2
MOTOROLA
Real Time Clock (RTC)
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Data Sheet
233