
SIM Bus Clock Control and Generation
MC68HC908GT16 MC68HC908GT8 Data Sheet, Rev. 3
Freescale Semiconductor
179
15.2 SIM Bus Clock Control and Generation
The bus clock generator provides system clock signals for the CPU and peripherals on the MCU. The
system clocks are generated from an incoming clock, CGMOUT, as shown in
Figure 15-3
. This clock
originates from either an external oscillator or from the internal clock generator.
Figure 15-3. System Clock Signals
15.2.1 Bus Timing
In user mode
,
the internal bus frequency is the internal clock generator output (CGMXCLK) divided by
four.
$FE03
SIM Break Flag Control
Register (SBFCR)
See page 193.
Read:
BCFE
R
R
R
R
R
R
R
Write:
Reset:
0
$FE04
Interrupt Status
Register 1 (INT1)
See page 187.
Read:
IF6
IF5
IF4
IF3
IF2
IF1
0
0
Write:
R
R
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
0
0
$FE05
Interrupt Status
Register 2 (INT2)
See page 188.
Read:
IF14
IF13
IF12
IF11
IF10
IF9
IF8
IF7
Write:
R
R
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
0
0
$FE06
Interrupt Status
Register 3 (INT3)
See page 188.
Read:
0
0
0
0
0
0
IF16
IF15
Write:
R
R
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
0
0
= Unimplemented
R
= Reserved
Addr.
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
Figure 15-2. SIM I/O Register Summary (Continued)
ICG
CGMXCLK
÷
2
BUS CLOCK
GENERATORS
SIM
ICG
SIM COUNTER
MONITOR MODE
CLOCK
SELECT
CIRCUIT
ICLK
CS
÷
2
A
B S*
CGMOUT
*WHEN S = 1,
CGMOUT = B
USER MODE
GENERATOR
ECLK
TBM PRESCALER
TBMCLK
COP PRESCALER
COPCLK