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© Motorola, Inc., 1998 EB263
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by EB263/D
Motorola Semiconductor Engineering Bulletin
EB263
How to Program Chip Selects on Modular Microcontrollers
with a System Integration Module
or a Single-Chip Integration Module
By Sharon Darley
Austin, Texas
Introduction
Modular MCUs with a system integration module (SIM) have 12 chip-
select lines, and those with a single-chip integration module (SCIM)
have nine chip selects. Both modules’
1
chip selects are programmed in
the same fashion.
These chip selects are used to expand the system. A chip-select signal
selects and enables a particular peripheral device or memory chip for
data transfer. The chip selects can also be programmed to generate
data transfer and size acknowledge (DSACK) signals.
The chip-select logic can wait for a certain number of states before
generating the acknowledgment. These states are called wait states.
The wait states are inserted after the S3 cycle of a read or write bus
cycle. A normal bus cycle lasts three clock cycles plus the number of wait
clock cycles. Up to and including 13 wait states can be inserted
automatically by the chip selects.
Frees
cale Semiconductor,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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