PXS20RM Datasheet, PDF (237/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

Chapter 12
Clock Monitor Unit (CMU)
Clock Monitor Unit (CMU)
12.1 Overview
The Clock Monitor Unit (CMU) serves three purposes:
• Selected clock monitoring: detect if the monitored clock leaves an upper or lower frequency
boundary
• XOSC clock monitoring: monitor the XOSC clock, which must be greater than the IRCOSC clock
divided by a division factor given by CMU_CSR[RCDIV]
• Frequency meter: measure the frequency of the IRCOSC clock versus the reference XOSC clock
frequency
When a failure is detected in one of the CMUs, by either the selected clock monitor or the XOSC monitor,
the CMU notifies the MC_RGM, the MC_ME, and the FCCU modules. The default behavior is such that
a reset occurs and a status bit is set in the MC_RGM. The user also has the option to change the behavior
of the action by disabling the reset and selecting an alternate action. The alternate action can be either
entering SAFE mode or generating an interrupt.
Table 12-1. CMU module summary
CMU_0
Module
CMU_1
CMU_2
System clock
XOSC
Motor control clock
FlexRay clock
Monitored clocks
12.2 Main features
• IRCOSC frequency measurement
• XOSC clock monitoring with respect to (IRCOSC clock)  n
• Selected clock frequency monitoring with respect to (IRCOSC clock)  4
• Event generation for various failures detected inside monitoring unit
12.3 Memory map and register description
The CMU registers are mapped through the MC_CGM (see the memory map in Chapter 11, Clock
Generation Module (MC_CGM)). The base address for each CMU is shown in Table 12-2.
Table 12-2. CMU base addresses
Module
Base address
CMU_0
CMU_1
CMU_2
0xC3FE_0100
0xC3FE_0120
0xC3FE_0140
Freescale Semiconductor
PXS20 Microcontroller Reference Manual, Rev. 1
12-1