Module Base Address Register (Mbar) - Motorola MC68340 User Manual

4.3.1 Module Base Address Register (MBAR)

MBAR 1
31 30 29 28
BA31 BA30 BA29 BA28
RESET:
0 0 0 0
MBAR 2
15 14 13 12
BA15 BA14 BA13 BA12
RESET
0 0 0 0
BA31–BA12—Base Address Bits 31–12
The base address field is the upper 20 bits of the MBAR that provides for block starting
locations in increments of 4-Kbytes.
Bits 11, 10—Reserved
AS8–AS0—Address Space Bits 8–0
The address space field allows particular address spaces to be masked, placing the 4K
module block into a particular address space(s). If an address space is masked, an
access to the register block location in that address space becomes an external access.
The module block is not accessed. The address space bits are as follows:
AS8—mask DMA Space
AS7—mask CPU Space
AS6—mask Supervisor Program
AS5—mask Supervisor Data
AS4—mask Reserved [Motorola]
AS3—mask Reserved [User]
AS2—mask User Program
AS1—mask User Data
AS0—mask Reserved [Motorola]
For each address space bit:
1 = Mask this address space from the internal module selection. The bus cycle goes
external.
0 = Decode for the internal module block.
V—Valid Bit
This bit indicates when the contents of the MBAR are valid. The base address value is
not used; therefore, all internal module registers are not accessible until the V-bit is set.
1 = Contents are valid.
0 = Contents are not valid.
4-20
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27 26 25 24
BA27 BA26 BA25 BA24
0 0 0 0
11 10 9 8
0 0 AS8 AS7
0 0 0 0
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23 22 21 20
BA23 BA22 BA21 BA20
0 0 0 0
7 6 5 4
AS6 AS5 AS4 AS3
0 0 0 0
address space (FC3–FC0 = 1xxx)
address space (FC3–FC0 = 0111)
address space (FC3–FC0 = 0110)
address space (FC3–FC0 = 0101)
address space (FC3–FC0 = 0100)
address space (FC3–FC0 = 0011)
address space (FC3–FC0 = 0010)
address space (FC3–FC0 = 0001)
address space (FC3–FC0 = 0000)
$0003FF00
19 18 17 16
BA19 IBA18 BA17 BA16
0 0 0 0
CPU Space Only
$0003FF02
3 2 1 0
AS2 AS1 AS0 V
0 0 0 0
CPU Space Only
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