Datasheet

Chapter 8 Internal Clock Generator (S08ICGV4)
MC9S08AW60 Data Sheet, Rev 2
146 Freescale Semiconductor
8.4.10 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 8-9 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.
Table 8-9. ICG State Table
Actual
Mode
(CLKST)
Desired
Mode
(CLKS)
Range
Reference
Frequency
(f
REFERENCE
)
Comparison
Cycle Time
ICGOUT
Conditions
1
for
CLKS = CLKST
1
CLKST will not update immediately after a write to CLKS. Several bus cycles are required before CLKST updates to the new
value.
Reason
CLKS1 ≠
CLKST
Off
(XX)
Off
(XX)
X0 — 0 — —
FBE
(10)
X 0 — 0 — ERCS = 0
SCM
(00)
SCM
(00)
X
f
ICGIRCLK
/7
2
2
The reference frequency has no effect on ICGOUT in SCM, but the reference frequency is still used in making the comparisons
that determine the DCOS bit
8/f
ICGIRCLK
ICGDCLK/R
Not switching
from FBE to
SCM
—
FEI
(01)
0
f
ICGIRCLK
/7
(1)
8/f
ICGIRCLK
ICGDCLK/R — DCOS = 0
FBE
(10)
X
f
ICGIRCLK
/7
(1)
8/f
ICGIRCLK
ICGDCLK/R — ERCS = 0
FEE
(11)
X
f
ICGIRCLK
/7
(1)
8/f
ICGIRCLK
ICGDCLK/R —
DCOS = 0 or
ERCS = 0
FEI
(01)
FEI
(01)
0
f
ICGIRCLK
/7 8/f
ICGIRCLK
ICGDCLK/R DCOS = 1 —
FEE
(11)
X
f
ICGIRCLK
/7 8/f
ICGIRCLK
ICGDCLK/R — ERCS = 0
FBE
(10)
FBE
(10)
X 0 — ICGERCLK/R ERCS = 1 —
FEE
(11)
X 0 — ICGERCLK/R —
LOCS = 1 &
ERCS = 1
FEE
(11)
FEE
(11)
0
f
ICGERCLK
2/f
ICGERCLK
ICGDCLK/R
3
3
After initial LOCK; will be ICGDCLK/2R during initial locking process and while FLL is re-locking after the MFD bits are changed.
ERCS = 1 and
DCOS = 1
—
1
f
ICGERCLK
128/f
ICGERCLK
ICGDCLK/R
(2)
ERCS = 1 and
DCOS = 1
—