MC9S08GB60 Datasheet, PDF (108/290 Pages) Motorola, Inc – Microcontrollers

Internal Clock Generator (ICG) Module
ICGS1 then writing 1 to ICGIF (LOCRE = 0), or by a loss-of-clock induced reset (LOCRE = 1), or by any
MCU reset.
If the ICG is in FEE, a loss of reference clock causes the ICG to enter SCM, and a loss of DCO clock causes
the ICG to enter FBE mode. If the ICG is in FBE mode, a loss of reference clock will cause the ICG to
enter SCM. In each case, the CLKST and CLKS bits will be automatically changed to reflect the new state.
A loss of clock will also cause a loss of lock when in FEE or FEI modes. Because the method of clearing
the LOCS and LOLS bits is the same, this would only be an issue in the unlikely case that LOLRE = 1 and
LOCRE = 0. In this case, the interrupt would be overridden by the reset for the loss of lock.
Table 7-2. Clock Monitoring
Mode
CLKS REFST
0X or 11
X
Off
10
0
10
1
0X
X
SCM
10
0
(CLKST = 00)
10
1
11
X
FEI
0X
X
(CLKST = 01)
11
X
FBE
10
0
(CLKST = 10)
10
1
FEE
(CLKST = 11)
11
X
ERCS
Forced Low
Forced Low
Real-Time⁽¹⁾
Forced Low
Forced High
Real-Time
Real-Time
Forced Low
Real-Time
Forced High
Real-Time
Real-Time
External Reference
Clock
Monitored?
No
No
Yes⁽¹⁾
No
No
Yes
Yes
No
Yes
No
Yes
Yes
DCO Clock
Monitored?
No
No
No
Yes⁽²⁾
Yes⁽²⁾
Yes⁽²⁾
Yes⁽²⁾
Yes
Yes
No
No
Yes
1. If ENABLE is high (waiting for external crystal start-up after exiting stop).
2. DCO clock will not be monitored until DCOS = 1 upon entering SCM from off or FLL bypassed external mode.
7.3.8 Clock Mode Requirements
A clock mode is requested by writing to CLKS1:CLKS0 and the actual clock mode is indicated by
CLKST1:CLKST0. Provided minimum conditions are met, the status shown in CLKST1:CLKST0 should
be the same as the requested mode in CLKS1:CLKS0. Table 7-3 shows the relationship between CLKS,
CLKST, and ICGOUT. It also shows the conditions for CLKS = CLKST or the reason CLKS ≠ CLKST.
NOTE
If a crystal will be used before the next reset, then be sure to set REFS = 1
and CLKS = 1x on the first write to the ICGC1 register. Failure to do so will
result in “locking” REFS = 0 which will prevent the oscillator amplifier
from being enabled until the next reset occurs.
MC9S08GB/GT Data Sheet, Rev. 2.3
108
Freescale Semiconductor