MC68332
SYSTEM INTEGRATION MODULE
USER’S MANUAL
4-15
4.3.3 External Bus Clock
The state of the external clock division bit (EDIV) in SYNCR determines clock rate for
the external bus clock signal (ECLK) available on pin ADDR23. ECLK is a bus clock
for MC6800 devices and peripherals. ECLK frequency can be set to system clock fre-
quency divided by eight or system clock frequency divided by sixteen. The clock is en-
abled by the CS10 field in chip select pin assignment register 1 (CSPAR1). ECLK
operation during low-power stop is described in the following paragraph. Refer to
for more information about the external bus clock.
4.3.4 Low-Power Operation
Low-power operation is initiated by the CPU32. To reduce power consumption selec-
tively, the CPU can set the STOP bits in each module configuration register. To mini-
mize overall microcontroller power consumption, the CPU can execute the LPSTOP
instruction, which causes the SIM to turn off the system clock.
When individual module STOP bits are set, clock signals inside each module are
turned off, but module registers are still accessible.
When the CPU executes LPSTOP, a special CPU space bus cycle writes a copy of
the current interrupt mask into the clock control logic. The SIM brings the MCU out of
low-power operation when either an interrupt of higher priority than the stored mask or
a reset occurs. Refer to
4.5.4.2 LPSTOP Broadcast Cycle
and
for more information.
101101
6029
12059
24117
48234
101110
6160
12321
24642
49283
101111
6291
12583
25166
50332
110000
6423
12845
25690
51380
110001
6554
13107
26214
52428
110010
6685
13369
26739
53477
110011
6816
13631
27263
54526
110100
6947
13894
27787
55575
110101
7078
14156
28312
56623
110110
7209
14418
28836
57672
110111
7340
14680
29360
58720
111000
7471
14942
2988
59769
111001
7602
15204
30409
60817
111010
7733
15466
30933
61866
111011
7864
15729
31457
62915
111100
7995
15991
31982
63963
111101
8126
16253
32506
65011
111110
8258
16515
33030
66060
111111
8389
16777
33554
67109
Table 4-8 System Frequencies from 32.768–kHz Reference (Continued)
To obtain clock frequency in kilohertz, find counter modulus in the left column, then multiply reference frequency by value
in appropriate prescaler cell.
Modulus
Prescaler
Y
[W:X] = 00
[W:X] = 01
[W:X] = 10
[W:X] = 11
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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