19-18
MCF5272 User’s Manual
Bus Control Signals
peripheral accesses, these outputs indicate that data is to be latched or driven onto a byte of
the data when driven low. BSn signals are asserted only to the memory bytes used during a
read or write access.
BSn signals are asserted during accesses to on-chip peripherals but not to on-chip SRAM,
cache, or ROM. During SDRAM accesses, these signals indicate a byte transfer between
SDRAM and the MCF5272 when driven high.
For SRAM or FLASH devices, BS[3:0] outputs should be connected to individual byte
strobe signals.
For SDRAM devices, BS[3:0] should be connected to individual SDRAM DQM signals.
Note that most SDRAMs associate DQM3 with the MSB, in which case BS3 should be
connected to the SDRAM's DQM3 input.
NOTE
In 16-bit bus mode, longword accesses are performed as two
sequential word accesses.
Table 19-5 shows how BS[3:0] should be connected to DQMx for 16- and 32-bit SDRAM
configurations.
Table 19-3. Byte Strobe Operation for 32-Bit Data Bus
BS3
BS2
BS1
BS0
Access Type
Data Located On
1
1
1
1
None
—
1
1
1
0
Byte
D[7:0]
1
1
0
1
D[15:8]
1
0
1
1
D[23:16]
0
1
1
1
D[31:24]
1
1
0
0
Word
D[15:0]
0
0
1
1
D[31:16]
0
0
0
0
Longword
D[31:0]
Table 19-4. Byte Strobe Operation for 16-Bit Data Bus
BS1
BS0
Access Type
Data Located On
1
1
None
—
1
0
Byte
D[7:0]
0
1
Byte
D[15:8]
0
0
Word
D[15:0]
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 ...