Datasheet

MC68331TS/D 29
Figure 9 Chip-Select Circuit Block Diagram
The following table lists allocation of chip-selects and discrete outputs on the pins of the MCU.
3.5.1 Chip-Select Registers
Pin assignment registers CSPAR0 and CSPAR1 determine functions of chip-select pins. These regis-
ters also determine port size (8- or 16-bit) for dynamic bus allocation.
A pin data register (PORTC) latches discrete output data.
Blocks of addresses are assigned to each chip-select function. Block sizes of 2 Kbytes to 1 Mbyte can
be selected by writing values to the appropriate base address register (CSBAR). Address blocks for
separate chip-select functions can overlap.
Chip-select option registers (CSORBT and CSOR[10:0]) determine timing of and conditions for asser-
tion of chip-select signals. Eight parameters, including operating mode, access size, synchronization,
and wait state insertion can be specified.
Initialization code often resides in a peripheral memory device controlled by the chip-select circuits. A
set of special chip-select functions and registers (CSORBT, CSBARBT) is provided to support bootstrap
operation.
Pin Chip Select Discrete Outputs
CSBOOT
CSBOOT —
BR
CS0 —
BG
CS1 —
BGACK
CS2 —
FC0 CS3
PC0
FC1 CS4
PC1
FC2 CS5
PC2
ADDR19 CS6
PC3
ADDR20 CS7
PC4
ADDR21 CS8
PC5
ADDR22 CS9
PC6
ADDR23 CS10
ECLK
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.
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