Chapter 20. Bus Operation
20-7
Data Transfer Mechanism
Figure 20-2. MCF5272 Interface to Various Port Sizes
The multiplexer takes the four bytes of the 32-bit bus and routes them to their required
positions. For example, OP3 can be routed to D[7:0], as would be the normal case when
interfacing to a 32-bit port. OP3 can be routed to D[23:16] for interfacing to a 16-bit port,
or it can be routed to D[31:24] for interfacing to an 8-bit port. The operand size, address,
and port size of the memory being accessed determines the positioning of bytes.
Table 20-3 describes data bus byte strobes. Note that most SDRAMs associate DQM3 with
the MSB, thus BS3 should be connected to the SDRAM's DQM3 input.
Table 20-3. Data Bus Byte Strobes
Transfer Size
Port Size
A[1:0]
BS3
BS2
BS1
BS0
D[31:24]
D[23:16]
D[15:8]
D[7:0]
Byte
8-bit (not
supported
for
SDRAM)
00
0
1
1
1
01
0
1
1
1
10
0
1
1
1
11
0
1
1
1
16-bit
00
0
1
1
1
01
1
0
1
1
10
0
1
1
1
11
1
0
1
1
32-bit
00
0
1
1
1
01
1
0
1
1
10
1
1
0
1
11
1
1
1
0
REGISTER
MULTIPLEXER
EXTERNAL
DATA BUS
ADDRESS
BYTE 0
INTERNAL TO
MCF5272
8-BIT PORT
16-BIT PORT
32-BIT PORT
BYTE 1
BYTE 2
BYTE 3
BYTE 0
BYTE 1
BYTE 2
BYTE 3
BYTE 0
BYTE 1
BYTE 2
BYTE 3
D[31:24]
D[23:16]
D[15:8]
D[7:0]
ROUTING AND DUPLICATION
OP0
OP1
OP2
OP3
A1
A0
0
0
0
0
1
0
0
0
0
1
1
0
1
1
Содержание DigitalDNA ColdFire MCF5272
Страница 1: ...MCF5272UM D Rev 0 02 2001 MCF5272 ColdFire Integrated Microprocessor User s Manual ...
Страница 38: ...xxxviii MCF5272 User s Manual TABLES Table Number Title Page Number ...
Страница 58: ...1 10 MCF5272 User s Manual MCF5272 Specific Features ...
Страница 90: ...2 42 MCF5272 User s Manual Exception Processing Overview ...
Страница 96: ...3 6 MCF5272 User s Manual MAC Instruction Execution Timings ...
Страница 158: ...5 46 MCF5272 User s Manual Motorola Recommended BDM Pinout ...
Страница 184: ...7 12 MCF5272 User s Manual Interrupt Controller Registers ...
Страница 338: ...13 44 MCF5272 User s Manual Application Examples ...
Страница 414: ...18 6 MCF5272 User s Manual PWM Programming Model ...
Страница 452: ...19 38 MCF5272 User s Manual Power Supply Pins ...
Страница 482: ...20 30 MCF5272 User s Manual Reset Operation ...
Страница 492: ...21 10 MCF5272 User s Manual Non IEEE 1149 1 Operation ...
Страница 548: ...INDEX Index 12 MCF5272 User s Manual ...