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System Integration Module
MOTOROLA
MC68328 DRAGONBALL PROCESSOR USER’S MANUAL
2-17
in the group-base mask register define the block size for the group. The base address field
is compared to the address on the address bus to determine if the group is decoded.
V
Valid Bit
This bit indicates the validity of the contents of its base address register and address mask
register pair. The programmed chip-selects do not assert until the V-bit is set. A reset
clears the V-bit in each base address register.
1 = Contents are valid
0 = Contents are not valid
2.5.2 Group-Base Address Mask Registers
These registers adjust the comparison range for the group. Bits in this register set to 1
always compare true with the corresponding address line.
GROUP BASE MASK (GMA31-GMA20)
0 = The corresponding address bit must match for a group to match
1 = The corresponding address bit compares true (don’t care)
These bits mask address A31 through A20. Usually, the group base address mask register
bits select the group size. For example, if all the mask bits are cleared, A31 to A20 are com-
pared against the value programmed in the group base address register. In this case, the
group has a 1 Mbyte space. If bit 4 (GMA20 bit) is set and the remainder of the bits are clear,
the group is selected if A31 to A21 are the same as the value programmed in the group-base
address register. This provides 2 Mbyte of space for the group. Further decoding is per-
formed for each chip-select by comparing lower address lines and the chip-select registers.
If the devices are small, it is possible to program the groups to the same space and use the
chip-select registers to decode the areas for each chip-select.
2.5.3 CHIP-SELECT REGISTERS
There are four 32-bit chip-select option registers in each chip-select group—one for each
chip-select signal.
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
GROUP BASE MASK (GMA31-GMA20)
UNUSED
GMA31 GMA30
GMA29
GMA28
GMA27
GMA26
GMA25
GMA24
GMA23
GMA22
GMA21
GMA20
0
0
0
0
Address: $(FF)FFF108, 10A, 10C, 10E
Reset Value: $0000
Figure 2-10. Group-Base Address Mask Registers
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
ADDRESS COMPARE A23-A16
UNUSED
BSW
AC23
AC22
AC21
AC20
AC19
AC18
AC17
AC16
-
-
-
-
-
-
-
-
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
ADDRESS MASK 23-16
UNUSED
RO
WAIT
AM23
AM22
AM21
AM20
AM19
AM18
AM17
AM16
-
-
-
-
-
-
-
-
Address: $(FF)FFF110, 114, 118, 11C, 120, 124, 128, 12C
Reset Value: $00010006
Figure 2-11. Chip-Select Registers for Group A and B
Summary of Contents for DragonBall MC68328
Page 5: ...vi MC68328 DRAGONBALL PROCESSOR USER S MANUAL MOTOROLA ...
Page 25: ...Overview 1 14 MC68328 DRAGONBALL PROCESSOR USER S MANUAL MOTOROLA ...
Page 45: ...System Integration Module 2 20 MC68328 DRAGONBALL PROCESSOR USER S MANUAL MOTOROLA ...
Page 103: ...Parallel Ports 7 16 MC68328 DRAGONBALL PROCESSOR USER S MANUAL MOTOROLA ...
Page 117: ...UART 8 14 MC68328 DRAGONBALL PROCESSOR USER S MANUAL MOTOROLA ...
Page 127: ...SPI Master 10 6 MC68328 DRAGONBALL PROCESSOR USER S MANUAL MOTOROLA ...