MC9S08QG8_09 Datasheet, PDF (75/314 Pages) Freescale Semiconductor, Inc – HCS08 Microcontrollers

Chapter 5 Resets, Interrupts, and General System Control
5.8.7 System Real-Time Interrupt Status and Control Register (SRTISC)
This high page register contains status and control bits for the RTI.
7
6
5
4
3
R RTIF
0
0
RTICLKS
RTIE
W
RTIACK
2
1
0
RTIS
Reset:
0
0
0
0
0
0
0
0
= Unimplemented or Reserved
Figure 5-9. System RTI Status and Control Register (SRTISC)
Table 5-10. SRTISC Register Field Descriptions
Field
Description
7
RTIF
6
RTIACK
5
RTICLKS
4
RTIE
2:0
RTIS
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.
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.
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.
Real-Time Interrupt Enable — This read-write bit enables real-time interrupts.
0 Real-time interrupts disabled.
1 Real-time interrupts enabled.
Real-Time Interrupt Delay Selects — These read/write bits select the period for the RTI. See Table 5-11.
Table 5-11. Real-Time Interrupt Period
RTIS2:RTIS1:RTIS0
Using Internal 1-kHz Clock Source^{1 2}
Using External Clock Source
Period = t_ext3
0:0:0
Disable RTI
Disable RTI
0:0:1
8 ms
t_ext x 256
0:1:0
32 ms
t_ext x 1024
0:1:1
64 ms
t_ext x 2048
1:0:0
128 ms
t_ext x 4096
1:0:1
256 ms
t_ext x 8192
1:1:0
512 ms
t_ext x 16384
1:1:1
1.024 s
t_ext x 32768
1 _{Values are shown in this column based on tRTI = 1 ms. See tRTI in the appendix Section A.8.1, “Control Timing,” for the}
tolerance of this value.
2 _{The initial RTI timeout period will be up to one 1-kHz clock period less than the time specified.}
3 _{text is the period of the external crystal frequency.}
MC9S08QG8 and MC9S08QG4 Data Sheet, Rev. 5
Freescale Semiconductor
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