Resets, Interrupts, and System Conguration
MC9S08RC/RD/RE/RG Data Sheet, Rev. 1.11
70
Freescale Semiconductor
5.8.6
System Real-Time Interrupt Status and Control Register (SRTISC)
This register contains one read-only status ag, one write-only acknowledge bit, three read/write delay
selects, and three unimplemented bits, which always read 0.
76543210
R
RTIF
0
RTICLKS
RTIE
0
RTIS2
RTIS1
RTIS0
W
RTIACK
Reset
00000000
= Unimplemented or Reserved
Figure 5-8. System RTI Status and Control Register (SRTISC)
Table 5-8. SRTISC Field Descriptions
Field
Description
7
RTIF
Real-Time Interrupt Flag — This read-only status bit indicates the periodic wakeup timer has timed out.
0 Periodic wakeup timer not timed out.
1 Periodic wakeup timer timed out.
6
RTIACK
Real-Time Interrupt Acknowledge — This write-only bit is used to acknowledge real-time interrupt request
(write 1 to clear RTIF). Writing 0 has no meaning or effect. Reads always return 0.
5
RTICLKS
Real-Time Interrupt Clock Select — This read/write bit selects the clock source for the real-time interrupt.
0 Real-time interrupt request clock source is internal 1-kHz oscillator.
1 Real-time interrupt request clock source is external clock.
4
RTIE
Real-Time Interrupt Enable — This read-write bit enables real-time interrupts.
0 Real-time interrupts disabled.
1 Real-time interrupts enabled.
2:0
RTIS[2:0]
Real-Time Interrupt Period Selects — These read/write bits select the wakeup period for the RTI. One clock
source for the real-time interrupt is its own internal clock source, which oscillates with a period of approximately
tRTI and is independent of other MCU clock sources. Using an external clock source the delays will be crystal
frequency divided by value in RTIS2:RTIS1:RTIS0. See
Table 5-9.Table 5-9. Real-Time Interrupt Period
RTIS2:RTIS1:RTIS0
Internal Clock Source (1)
(tRTI = 1 ms, Nominal)
External Clock Source (2)
Period = text
2. text is based on the external clock source, resonator, or crystal selected by the ICG conguration. See Table A-9 for details. 0:0:0
Disable periodic wakeup timer
0:0:1
8 ms
text x 256
0:1:0
32 ms
tex x 1024
0:1:1
64 ms
tex x 2048
1:0:0
128 ms
tex x 4096
1:0:1
256 ms
text x 8192
1:1:0
512 ms
text x 16384
1:1:1
1.024 s
tex x 32768