MC68020 Motorola, MC68020 Datasheet - Page 53

• Manufacturer Part Number: MC68020
• Description: (MC68020 / MC68EC020) MICROPROCESSORS USERS MANUAL
• Manufacturer: Motorola

Figure 5-4 shows the required organization of data ports on the MC68020/EC020 bus for
8-, 16-, and 32-bit devices. The four bytes shown in Figure 5-4 are connected through the
internal data bus and data multiplexer to the external data bus. This path is the means
through which the MC68020/EC020 supports dynamic bus sizing and operand
misalignment. Refer to 5.2.2 Misaligned Operands for the definition of misaligned
operand. The data multiplexer establishes the necessary connections for different
combinations of address and data sizes.
5-6
INCREASING
ADDRESSES
MEMORY
EXTERNAL DATA BUS
MULTIPLEXER
LONG-WORD OPERAND
REGISTER
ADDRESS
xxxxxxx0
xxxxxxx0
xxxxxxx0
Figure 5-4. MC68020/EC020 Interface to Various Port Sizes
2
2
1
3
Figure 5-3. Internal Operand Representation
D31– D24
BYTE 0
BYTE 0
BYTE 2
BYTE 0
BYTE 1
BYTE 2
BYTE 3
OP0
0
31
OP0
8-BIT PORT
M68020 USER’S MANUAL
D23–D16
BYTE 1
BYTE 3
BYTE 1
ROUTING AND DUPLICATION
OP1
1
WORD OPERAND
OP1
16-BIT PORT
D15–D8
BYTE 2
OP2
2
15
BYTE OPERAND
OP2
OP2
D7–D0
BYTE 3
OP3
3
7
OP3
OP3
OP3
32-BIT PORT
THE MC68020/EC020
EXTERNAL BUS
0
0
0
INTERNAL TO
MOTOROLA