On-chip reference clock automatic selection circuit

Abstract

The invention provides an on-chip reference clock automatic selection circuit. The on-chip reference clock automatic selection circuit comprises an on-chip reference clock module, an off-chip clock signal, an input power, a power on reset module, a clock counting module and a clock selection module; wherein the on-chip reference clock module produces an on-chip reference clock signal; the power onreset module generates a power on reset signal when the input power is supplied; and the clock counting module detects the number of the clock edges of the off-chip clock signal when the power on reset signal hops; when the number of the clock edges does not reach a preset value, the clock selection module selects the on-chip reference clock signal as the output clock, otherwise, the clock selection module selects the off-chip clock signal as the output clock.

Description

technical field [0001] The invention relates to a selection circuit, in particular to an automatic selection circuit for an on-chip reference clock. Background technique [0002] With the continuous development of the integrated circuit industry, the integration of the system is getting higher and higher. Many integrated circuit chips integrate on-chip reference clock modules. The on-chip reference clock module generates on-chip reference clock signals through on-chip circuits, independent of Quartz crystal outside the chip to achieve the purpose of reducing cost and volume. In order to maintain compatibility, these integrated circuit chips also retain an off-chip clock signal input, which involves the selection of the clock signal. In order to achieve switching between the off-chip clock and the on-chip reference clock, a clock selection signal is required. Complete, the clock selection signal of the prior art is generally a static signal, configured in advance by the user...

AI Technical Summary

Problems solved by technology

In order to maintain compatibility, these integrated circuit chips also retain an off-chip clock signal input, which involves the selection of the clock signal. In order to achieve switching between the off-chip clock and the on-chip reference clock, a clock selection signal is required. Complete, the clock selection signal of the prior art is generally a static signal, configured in advance by the user according to needs, to determine whether to use the on-chip reference clock signal or the off-chip clock signal as the on-chip clock source of the chip, which cannot be based on the off-chip clock signal The presence or absence of the clock selection signal from the automatic generation

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