Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of networking-chip designer PMC-Sierra (Nasdaq: PMCS) fell more than 13% on tremendously heavy volume in intraday trading action.

So what: PMC's fourth quarter beat analyst expectations any way you look at it, but the coming quarter looks weak with falling sales where the Street wanted a continued rise. Management motivated the cautious guidance with "current levels of demand" and order patterns.

Now what: Management says that the storage-chip segment should recover quickly as large new customers NetApp (Nasdaq: NTAP) and IBM (NYSE: IBM) get up to speed with their PMC orders. That leaves networking to explain the dour outlook, which most likely translates into weak orders from Cisco Systems (Nasdaq: CSCO) and Alcatel-Lucent (NYSE: ALU), who make up the majority of that division's revenue. Look for earnings reports out of those companies to either confirm or counteract PMC's predictions.

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Fool contributor Anders Bylund holds no position in any of the companies discussed here. The Fool has created a bull call spread position on Cisco Systems. The Fool owns shares of International Business Machines. Motley Fool Alpha owns shares of Cisco Systems. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool is investors writing for investors.