Chapter 20. Bus Operation
20-9
Data Transfer Mechanism
Table 20-5 lists the transfer size, A[1:0], and the corresponding pattern of the data transfer
for write cycles from the internal multiplexer of the MCF5272 to the external data bus. For
example, if a longword transfer is generated to a 16-bit port, the MCF5272 starts the cycle
with A[1:0] set to 0x0 and reads the first word. The address in then incremented to 0x2 and
the second word is read. The data for both word reads is taken from D[31:16]. Bytes labeled
“X” are don’t cares.I
Table 20-4. Data Bus Requirement for Read Cycles
Transfer Size
A[1:0]
External Data Bytes Required
32-Bit Port
16-Bit Port
8-Bit Port
D[31:24]
D[23:16]
D[15:8]
D[7:0]
D[31:24]
D[23:16]
D[31:24]
Byte
00
Byte 0
X
X
X
Byte 0
X
Byte 0
01
X
Byte 1
X
X
X
Byte 1
Byte 1
10
X
X
Byte 2
X
Byte 2
X
Byte 2
11
X
X
X
Byte 3
X
Byte 3
Byte 3
Word
00
Byte 0
Byte 1
X
X
Byte 0
Byte 1
Byte 0
01
—
—
—
—
—
—
Byte 1
10
X
X
Byte2
Byte 3
Byte 2
Byte 3
Byte 2
11
—
—
—
—
—
—
Byte 3
Longword
00
Byte 0
Byte 1
Byte 2
Byte 3
Byte 0
Byte 1
Byte 0
01
—
—
—
—
—
—
Byte 1
10
—
—
—
—
Byte 2
Byte 3
Byte 2
11
—
—
—
—
—
—
Byte 3
Line
00
Byte 0
Byte 1
Byte 2
Byte 3
Byte 0
Byte 1
Byte 0
01
—
—
—
—
—
—
Byte 1
10
—
—
—
—
Byte 2
Byte 3
Byte 2
11
—
—
—
—
—
—
Byte 3
Table 20-5. Internal to External Data Bus Multiplexer–Write Cycle
Transfer Size
A[1:0]
External Data Bus Connection
D[31:24]
D[23:16]
D[15:8]
D[7:0]
Byte 00
OP3
X
X
X
01
OP3
OP3
X
X
10
OP3
X
OP3
X
11
OP3
OP3
X
OP3
Word 00
OP2
OP3
X
X
01
OP3
X
X
X
10
OP2
OP3
OP2
OP3
11
OP3
X
X
X
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 ...