MC68340AB16E Datasheet, PDF (128/441 Pages) Motorola, Inc – Integrated Processor with DMA User’s Manual

Freescale Semiconductor, Inc.
NCS—No CPU Space
This bit specifies whether or not a chip select will assert on a CPU space access cycle
(FC3–FC0 = $7 or $F). If both supervisor data and program accesses are desired, while
ignoring CPU space accesses, then this bit should be set. The NCS bit is cleared at
reset.
1 = Suppress the chip select on a CPU space access.
0 = Assert the chip select on a CPU space access.
V—Valid Bit
This bit indicates that the contents of its base address register and address mask
register pair are valid. The programmed chip selects do not assert until the V-bit is set.
A reset clears the V-bit in each base address register, but does not change any other
bits in the base address and address mask registers (CS0 is a special case, see 4.2.4.2
Global Chip Select Operation).
1 = Contents are valid.
0 = Contents are not valid.
4.3.4.2 ADDRESS MASK REGISTERS. There are four 32-bit address mask registers in
the chip select function, one for each chip select signal.
Address Mask 1
31
30
29
28
AM31 AM30 AM29 AM28
RESET:
U
U
U
U
27
AM27
U
26
AM26
U
25
AM25
U
24
AM24
U
23
AM23
U
22
AM22
U
21
AM21
U
$040, $048, $050, $058
20
19
18
17
16
AM20 AM19 AM18 AM17 AM16
U
U
U
U
U
Supervisor Only
Address Mask 2
15
14
13
12
11
10
9
AM15 AM14 AM13 AM12 AM11 AM10 AM9
RESET:
U
U
U
U
U
U
U
U = Unaffected by reset
$042, $04A, $052, $05A
8
7
6
5
4
3
2
1
0
AM8 FCM3 FCM2 FCM1 FCM0 DD1 DD0 PS1 PS0
U
U
U
U
U
U
U
U
U
Supervisor Only
AM31–AM8—Address Mask Bits 31–8
The address mask field, the upper 24 bits of each address mask register, defines the
chip select block size. The block size is equal to 2ⁿ, where n = (number of bits set in
the address mask field) + 8.
Any set bit masks the corresponding base address register bit (the base address
register bit becomes a don’t care). By masking the address bits independently, external
devices of different size address ranges can be used. Address mask bits can be set or
cleared in any order in the field, allowing a resource to reside in more than one area of
the address map. This field can be read or written at any time.
MOTOROLA
MC68340 USER’S MANUAL
4-31
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