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MC68302FC20 Datasheet(PDF) 43 Page - Motorola, Inc

Part No. MC68302FC20
Description  Integrated Multiprotocol Processor User’s Manual
Download  480 Pages
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Maker  MOTOROLA [Motorola, Inc]
Homepage  http://www.freescale.com
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MC68302FC20 Datasheet(HTML) 43 Page - Motorola, Inc

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MC68000/MC68008 Core
MOTOROLA
MC68302 USER’S MANUAL
2-13
try is $0F0; however, the actual BAR is a 16-bit value within the BAR entry and is located at
$0F2.
After a total system reset, the on-chip peripheral base address is undefined, and it is not
possible to access the on-chip peripherals at any address until BAR is written. The BAR and
the SCR can always be accessed at their fixed addresses.
NOTE
The BAR, SCR and CKCR registers are internally reset only
when a total system reset occurs by the simultaneous assertion
of RESET and HALT. The chip-select (CS) lines are not assert-
ed on accesses to these locations. Thus, it is very helpful to use
CS lines to select external ROM/RAM that overlaps the BAR and
SCR register locations, since this prevents potential bus conten-
tion. (The internal access (IAC) signal may also be used to pre-
vent bus contention.)
NOTE
In 8-bit system bus operation, IMP accesses are not possible un-
til the low byte of the BAR is written. Since the MOVE.W instruc-
tion writes the high byte followed by the low byte, this instruction
guarantees the entire word is written.
Do not assign other devices on the system bus an address that falls within the address
range of the peripherals defined by the BAR. If this happens, BERR is generated (if the ad-
dress decode conflict enable (ADCE) bit is set) and the address decode conflict (ADC) bit in
the SCR is set.
The BAR is a 16-bit, memory-mapped, read-write register consisting of the high address
bits, the compare function code bit, and the function code bits. Upon a total system reset, its
value may be read as $BFFF, but its value is not valid until written by the user. The address
of this register is fixed at $0F2 in supervisor data space. BAR cannot be accessed in user
data space.
Bits 15–13—FC2–FC0
The FC2–FC0 field is contained in bits 15–13 of the BAR. These bits are used to set the
address space of 4K-byte block of on-chip peripherals. The address compare logic uses
these bits, dependent upon the CFC bit, to cause an address match within its address
space.
NOTE
Do not assign this field to the M68000 core interrupt acknowl-
edge space (FC2–FC0 = 7).
15
13
12
11
0
FC2–FC0
CFC
BASE ADDRESS
23
22
21
20
19
18
17
16
15
14
13
12


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