Datasheet

Chapter 5 Resets, Interrupts, and General System Control
MC9S08QG8 and MC9S08QG4 Data Sheet, Rev. 5
Freescale Semiconductor 73
5.8.7 System Real-Time Interrupt Status and Control Register (SRTISC)
This high page register contains status and control bits for the RTI.
76543210
RRTIF 0
RTICLKS RTIE
0
RTIS
W RTIACK
Reset:00000000
= Unimplemented or Reserved
Figure 5-9. System RTI Status and Control Register (SRTISC)
Table 5-10. SRTISC Register 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
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
1
Values are shown in this column based on t
RTI
= 1 ms. See t
RTI
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.
Using External Clock Source
Period = t
ext
3
3
t
ext
is the period of the external crystal frequency.
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