Motorola MC68340 User Manual page 127

4.3.4.1 BASE ADDRESS REGISTERS. There are four 32-bit base address registers in
the chip select function, one for each chip select signal.
Base Address 1
31 30 29 28
BA31 BA30 BA29 BA28
RESET:
U U U U
Base Address 2
31 30 29 28
BA15 BA14 BA13 BA12
RESET:
U U U U
U = Unaffected by reset
BA31–BA8—Base Address Bits 31–8
The base address field, the upper 24 bits of each base address register, selects the
starting address for the chip select. The specified base address must be on a multiple of
the selected block size. The corresponding bits, AM31–AM8, in the address mask
register define the size of the block for the chip select. The base address field (and the
base function code field) is compared to the address on the address bus to determine if
a chip select should be generated.
BFC3–BFC0—Base Function Code Bits 3–0
The value programmed into this field causes a chip select to be asserted for a certain
address space type. There are nine function code address spaces (see Section 3 Bus
Operation) specified as either user or supervisor, program or data, CPU, and DMA.
These bits should be used to allow access to one type of address space. If access to
more than one type of address space is desired, the FCMx bits should be used in
addition to the BFCx bits. To prevent access to CPU space, set the NCS bit.
WP—Write Protect
This bit can restrict write accesses to the address range in a base address register. An
attempt to write to the range of addresses specified in a base address register that has
this bit set returns BERR .
1 = Only read accesses are allowed.
0 = Either read or write accesses are allowed.
FTE—Fast-Termination Enable
This bit causes the cycle to terminate early with an internal DSACK , giving a fast two-
clock external access. When clear, all external cycles are at least three clocks. If fast
termination is enabled, the DD bits of the corresponding address mask register are
overridden (see Section 3 Bus Operation).
1 = Fast termination cycle enabled (termination determined by PS bits).
0 = Fast termination cycle disabled (termination determined by DD and PS bits).
4-30
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27 26 25 24
BA27 BA26 BA25 BA24
U U U U
27 26 25 24
BA11 BA10 BA9 BA8
U U U U
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$044, $04C, $054, $05C
23 22 21 20
BA23 BA22 BA21 BA20
U U U U
$046, $04E, $056, $05E
23 22 21 20
BFC3 BFC2 BFC1 BFC0
U U U U
19 18 17 16
BA19 BA18 BA17 BA16
U U U U
Supervisor Only
19 18 17 16
WP FTE NCS V
U U 0 0
Supervisor Only
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