Motorola MCF5281, MCF5282 user manual Low-Power Wakeup Operation

Models: MCF5282 MCF5281

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Low-Power Wakeup Operation

10.5 Low-Power Wakeup Operation

The System Control Module (SCM) contains an 8-bit low-power interrupt control register (LPICR) used explicitly for controlling the low-power stop mode. This register must explicitly be programmed by software to enter low-power mode.

Each interrupt controller provides a special combinatorial logic path to provide a special wake-up signal to exit from the low-power stop mode. This special mode of operation works as follows:

First, LPICR[6:4] is loaded with the mask level that will be specified while the core is in stop mode. LPICR[7] must be set to enable this mode of operation.

NOTE

The wakeup mask level taken from LPICR[6:4] is adjusted by hardware to allow a level 7 IRQ to generate a wakeup. That is, the wakeup mask value used by the interrupt controller must be in the range of 0–6.

Second, the processor executes a STOP instruction which places it in stop mode. Once the processor is stopped, each interrupt controller enables a special logic path which evaluates the incoming interrupt sources in a purely combinatorial path; that is, there are no clocked storage elements. If an active interrupt request is asserted and the resulting interrupt level is greater than the mask value contained in LPICR[6:4], then each interrupt controller asserts the wake-up output signal, which is routed to the SCM where it is combined with the wakeup signals from the other interrupt controller and then to the PLL module to re-enable the device’s clock trees and resume processing.

MOTOROLA

Chapter 10. Interrupt Controller Modules

10-17

Page 245
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Motorola MCF5281, MCF5282 user manual Low-Power Wakeup Operation