Specifications

Standard Initialization Sequence for Hercules Microcontrollers

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2.4 Configure Oscillator Monitor

The HF LPO clock source is used as a reference clock for monitoring the main oscillator. A failure is

detected if the oscillator frequency falls outside the range: {f

HFLPO

/ 4, f

HFLPO

*4}.

The HF LPO frequency varies significantly over process corners as well as with changes in the core

supply (VCC) and temperature. The Hercules microcontrollers allow the application to trim the HF LPO

such that the application can choose the operating frequency point of the HF LPO. This in turn determines

the valid range of oscillator frequency.

During device test, a trim value is written into the one-time programmable section of the Flash memory

(OTP), address 0xF008_01B4. Bits 31:16 of this OTP word contain a 16-bit value that may be

programmed into Low Power Oscillator Monitor Control Register (LPOMONCTL) in order to initialize the

trim for HF LPO.

Alternatively the application can use the dual-clock compare (DCC) module to determine the trim setting

for the HF LPO. The DCC module allows for comparison of two clock frequencies. Once the HF LPO is

determined to be in-range with the initial HFTRIM setting from the OTP, the crystal oscillator may be used

as a reference against which the HF LPO and LF LPO may be further adjusted. For more details, see the

specific part's technical reference manual.

Initialization of Hercules™ ARM

Cortex™-R4F Microcontrollers SPNA106– September 2011

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