MC68332
SYSTEM INTEGRATION MODULE
USER’S MANUAL
4-51
in the corresponding option register is programmed to a nonzero value, selecting a
transfer size. The chip-select option must not be written until a base address has been
written to a proper base address register. CSBOOT is automatically asserted out of
reset. Alternate functions for chip-select pins are enabled if appropriate data bus pins
are held low at the release of the reset signal (refer to
for more information).
is a functional diagram of a single chip-select
circuit.
Figure 4-18 Chip-Select Circuit Block Diagram
4.8.1 Chip-Select Registers
Each chip-select pin can have one or more functions. Chip-select pin assignment reg-
isters (CSPAR[0:1]) determine functions of the pins. Pin assignment registers also de-
termine port size (8- or 16-bit) for dynamic bus allocation. A pin data register (PORTC)
latches data for chip-select pins that are used for discrete output.
Blocks of addresses are assigned to each chip-select function. Block sizes of two
Kbytes to one Mbyte can be selected by writing values to the appropriate base address
register (CSBAR[0:10], CSBARBT). Address blocks for separate chip-select functions
can overlap.
Chip select option registers (CSOR[0:10], CSORBT) determine timing of and condi-
tions for assertion of chip-select signals. Eight parameters, including operating mode,
access size, synchronization, and wait state insertion can be specified.
Initialization software usually resides in a peripheral memory device controlled by the
chip-select circuits. A set of special chip-select functions and registers (CSORBT, CS-
BARBT) is provided to support bootstrap operation.
Comprehensive address maps and register diagrams are provided in
CHIP SEL BLOCK
AVEC
GENERATOR
DSACK
GENERATOR
PIN
ASSIGNMENT
REGISTER
PIN
DATA
REGISTER
BASE ADDRESS REGISTER
TIMING
AND
CONTROL
ADDRESS COMPARATOR
OPTION COMPARE
OPTION REGISTER
AVEC
DSACK
PIN
BUS CONTROL
INTERNAL
SIGNALS
ADDRESS
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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