Datasheet

Resets, Interrupts, and System Configuration
MC9S08GT16A/GT8A Data Sheet, Rev. 1
76 Freescale Semiconductor
5.7.6 System Real-Time Interrupt Status and Control Register (SRTISC)
This register contains one read-only status flag, 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 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
t
RTI
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
(t
RTI
= 1.15 ms, Nominal)
1
See Table A-12 t
RTI
in Appendix A, “Electrical Characteristics,” for the tolerance on these values.
External Clock Source
2
Period = t
ext
2
t
ext
is based on the external clock source, resonator, or crystal selected by the ICG configuration. See Table A-11 for details.
0:0:0 9.2 ms Disable periodic wakeup timer
0:0:1 18.4 ms
t
ext
x 256
0:1:0 36.8 ms
t
ex
x 1024
0:1:1 73.6 ms
t
ex
x 2048
1:0:0 147.2 ms
t
ex
x 4096
1:0:1 294.4 ms
t
ext
x 8192
1:1:0 588.8 ms
t
ext
x 16384
1:1:1 1177.6 ms
t
ex
x 32768