MC68HC908LJ12 Datasheet, PDF (218/413 Pages) Freescale Semiconductor, Inc – 8-bit microcontroller units

Real Time Clock (RTC)
XTL[2:0] — Crystal Frequency Select Bits
These three bits set the prescalers/dividers for proper operation of the
RTC module for various crystal (CGMXCLK) input frequencies. The
XTL[2:0] bits can only be written once after reset, subsequent writes
to these bits will have no effect on its content. Table 12-1 shows the
XTL[2:0] settings for various CGMXCLK frequencies. Reset clear the
XTL[2:0] bits.
Table 12-1. CGMXCLK Frequency for RTC Input Reference
CGMXCLK⁽¹⁾
XTL2
XTL1
XTL0
32.768 kHz
0
0
0
Reserved
0
0
1
32.000 kHz
0
1
0
38.400 kHz
0
1
1
64.000 kHz
1
X
0
76.800 kHz
1
X
1
Notes:
1. Using crystal frequencies other than these specified will cause incorrect timings in the RTC
module.
12.6.3 RTC Status Register (RTCSR)
The RTC status register contains eight status flags. When a flag is set
and the corresponding interrupt enable bit is also set, a CPU interrupt
request is generated.
Address: $0044
Read: ALMF CHRF DAYF
HRF
MINF SECF TB1F
TB2F
Write:
Reset: 0
0
0
0
0
0
0
0
= Unimplemented
Figure 12-5. RTC Status Register (RTCSR)
MC68HC908LJ12 — Rev. 2.1
Freescale Semiconductor
Real Time Clock (RTC)
Technical Data
219