Chapter 19. Signal Descriptions
19-19
Bus Control Signals
19.5.3 Read/Write (R/W)
R/W is programmed on a per-chip-select basis for use with SRAM and external peripheral
write accesses. It should be connected to the external peripheral or memory write enable
signal.
R/W acts as a write strobe to external SRAM when the decoded chip select is configured
for either of the two SRAM/ROM modes. It is asserted during on-chip peripherals accesses
and negated during on-chip SRAM accesses.
19.5.4 Transfer Acknowledge (TA/PB5)
Assertion of the transfer acknowledge (TA/PB5) input terminates an external bus cycle. It
is enabled on a per chip select basis by programming the wait state field to 0x1F in the
corresponding chip select option register (CSORn[WS]). This pin requires a 4.7-K
Ω
pull-up resistor or external logic that drives inactive high.
TA must always be returned high before it can be detected again. Asserting TA into the next
bus cycle has no effect and does not terminate the bus cycle.
NOTE:
Even though EBI modes set to SDRAM require setting the wait
state field in the chip select option register to 31, a low signal
should never be applied to TA during such accesses. For
SDRAM accesses the bus cycle is terminated internally by
circuitry in the SDRAM module.
19.5.5 Hi-Z
Hi-Z is a test signal. When it is connected to GND during reset, all output pins are driven
to high impedance. A 4.7-K
Ω
pullup resistor should be connected to this signal if the Hi-Z
function is not used.
Table 19-5. Connecting BS[3:0] to DQMx
5272 SDRAM
Data Signals
16 Bit
32 Bit
16 Bit
32 Bit (2 x 16)
32 Bit (1 x 32)
BS3
BS3
DQMH
DQMH
DQM3
D[31:24]
BS2
BS2
DQML
DQML
DQM2
D[23:16]
NC
BS1
NC
DQMH
DQM1
D[15:8]
NC
BS0
NC
DQML
DQM0
D[7:0]
Содержание DigitalDNA ColdFire MCF5272
Страница 1: ...MCF5272UM D Rev 0 02 2001 MCF5272 ColdFire Integrated Microprocessor User s Manual ...
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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 ...