MOTOROLA
MC68341 USER’S MANUAL
4- 15
4.2.3.3 CLOCK CONTROL. The clock control circuits determine the source used for both
internal and external clocks during special circumstances, such as low-power stop
(LPSTOP) execution.
Table 4-3 summarizes the clock activity during LPSTOP in crystal mode operation. Any
clock in the off state is held low. The STEXT and STSIM bits in the SYNCR control clock
activity during LPSTOP. Refer to 4.2.6 Low-Power Stop for additional information.
Table 4-3. Clock Control Signals
Control Bits
Clock Outputs
STSIM
STEXT
SIMCLK
CLKOUT
0
EXTAL
Off
0
1
EXTAL
1
0
VCO
Off
1
VCO
NOTE: SIMCLK runs the periodic interrupt RESET and
IRQ≈ pin synchronizers in LPSTOP mode.
4.2.4 Chip Select Operation
Typical microprocessor systems require external hardware to provide select signals to
external memory and peripherals. The MC68341 integrates these functions on chip to
provide the cost, speed, and reliability benefits of a higher level of integration. The chip
select function contains register pairs for each external chip select signal. The pair
consists of a base address register and an address mask register that define the
characteristics of a single chip select. The register pair provides flexibility for a wide
variety of chip select functions.
There are also two registers associated with each chip select to support 68000 bus
operation. The bus select register defines the type of bus cycle for each chip select. The
map select register defines the 68000 bus byte peripherals.
4.2.4.1 PROGRAMMABLE FEATURES. The chip select function supports the following
programmable features:
Eight Programmable Chip Select Circuits
All eight chip select circuits are independently programmable from the same list of
selectable features. Each chip select circuit has an individual base address register and
address mask register that contain the programmed characteristics of that chip select.
The base address register selects the starting address for the address block in 256-byte
increments. The address mask register specifies the size of the address block range.
The base address register V-bit indicates that the register information for that chip
select is valid. A global chip select (CS0 ) allows address decode for a boot ROM before
system initialization occurs.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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