Functional Description - NXP Semiconductors freescale KV4 Series Reference Manual

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24.4.4 Compare High Register (EWM_CMPH)

The CMPH register is reset to 0xFF after a CPU reset. This provides a maximum of 256

clocks time, for the CPU to service the EWM counter.

This register can be written only once after a CPU reset.

Writing this register more than once generates a bus transfer

The valid values for CMPH are up to 0xFE because the EWM

counter never expires when CMPH = 0xFF. The expiration

happens only if EWM counter is greater than CMPH.

Address: 4006_1000h base + 3h offset = 4006_1003h

To prevent runaway code from changing this field, software should write to this field after a CPU reset

even if the (default) maximum service time is required.

24.5 Functional Description

The following sections describe functional details of the EWM module.

24.5.1 The EWM_out Signal

The EWM_out is a digital output signal used to gate an external circuit (application

specific) that controls critical safety functions. For example, the EWM_out could be

connected to the high voltage transistors circuits that control an AC motor in a large

The EWM_out signal remains deasserted when the EWM is being regularly serviced by

the CPU within the programmable service window, indicating that the application code is

executed as expected.

Freescale Semiconductor, Inc.

EWM_CMPH field descriptions

KV4x Reference Manual, Rev. 2, 02/2015

Chapter 24 External Watchdog Monitor (EWM)