EM773 datasheet(13/45 Pages) NXP

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EM773

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Objective data sheet

Rev. 1 — 1 September 2010

13 of 45

NXP Semiconductors

EM773

Energy metering IC

• Four match registers per timer that allow:

– Continuous operation with optional interrupt generation on match.

– Stop timer on match with optional interrupt generation.

– Reset timer on match with optional interrupt generation.

• Up to four external outputs corresponding to match registers, with the following

capabilities:

– Set LOW on match.

– Set HIGH on match.

– Toggle on match.

– Do nothing on match.

7.13 System tick timer

The ARM Cortex-M0 includes a system tick timer (SYSTICK) that is intended to generate

a dedicated SYSTICK exception at a fixed time interval (typically 10 ms).

7.14 Watchdog timer

The purpose of the watchdog is to reset the microcontroller within a selectable time

period.

7.14.1 Features

• Internally resets chip if not periodically reloaded.

• Debug mode.

• Enabled by software but requires a hardware reset or a watchdog reset/interrupt to be

disabled.

• Incorrect/Incomplete feed sequence causes reset/interrupt if enabled.

• Flag to indicate watchdog reset.

• Programmable 24-bit timer with internal prescaler.

• Selectable time period from (Tcy(WDCLK) × 256 × 4) to (Tcy(WDCLK) × 224 × 4) in

multiples of Tcy(WDCLK) × 4.

• The Watchdog Clock (WDCLK) source can be selected from the Internal RC oscillator

(IRC), the Watchdog oscillator, or the main clock. This gives a wide range of potential

timing choices of Watchdog operation under different power reduction conditions. It

also provides the ability to run the WDT from an entirely internal source that is not

dependent on an external crystal and its associated components and wiring for

increased reliability.

7.15 Clocking and power control

7.15.1 Crystal oscillators

The EM773 includes three independent oscillators. These are the system oscillator, the

Internal RC oscillator (IRC), and the Watchdog oscillator. Each oscillator can be used for

more than one purpose as required in a particular application.

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