MCF5271 查看數據表（PDF） - Freescale Semiconductor

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MCF5271

MCF5271 Integrated Microprocessor Hardware Specification

Freescale Semiconductor 

Design Recommendations

5.2.2 WAIT Mode

WAIT mode is intended to be used to stop only the CPU core and memory clocks until a wakeup event is

detected. In this mode, peripherals may be programmed to continue operating and can generate interrupts,

which cause the CPU core to exit from WAIT mode.

5.2.3 DOZE Mode

DOZE mode affects the CPU core in the same manner as WAIT mode, but with a different code on the

CIM LPMD bits, which are monitored by the peripherals. Each peripheral defines individual operational

characteristics in DOZE mode. Peripherals which continue to run and have the capability of producing

interrupts may cause the CPU to exit the DOZE mode and return to the RUN mode. Peripherals which are

stopped will restart operation on exit from DOZE mode as defined for each peripheral.

5.2.4 STOP Mode

STOP mode affects the CPU core in the same manner as the WAIT and DOZE modes, but with a different

code on the CCM LPMD bits. In this mode, all clocks to the system are stopped and the peripherals cease

operation.

STOP mode must be entered in a controlled manner to ensure that any current operation is properly

terminated. When exiting STOP mode, most peripherals retain their pre-stop status and resume operation.

5.2.5 Peripheral Shut Down

Most peripherals may be disabled by software in order to cease internal clock generation and remain in a

static state. Each peripheral has its own specific disabling sequence (refer to each peripheral description

for further details). A peripheral may be disabled at anytime and will remain disabled during any low

power mode of operation.

6 Design Recommendations

6.1 Layout

• Use a 4-layer printed circuit board with the VDD and GND pins connected directly to the power

and ground planes for the MCF5271.

• See application note AN1259 System Design and Layout Techniques for Noise Reduction in

processor-Based Systems.

• Match the PC layout trace width and routing to match trace length to operating frequency and

board impedance. Add termination (series or therein) to the traces to dampen reflections.

Increase the PCB impedance (if possible) keeping the trace lengths balanced and short. Then do

cross-talk analysis to separate traces with significant parallelism or are otherwise "noisy". Use 6

mils trace and separation. Clocks get extra separation and more precise balancing.

MCF5271 Integrated Microprocessor Hardware Specification, Rev. 1.2

Freescale Semiconductor

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