Research in Motion said on Friday it would take a big charge in its third quarter to write down the value of its poorly received PlayBook tablet computers, in a fresh setback for the struggling BlackBerry maker.

The Waterloo, Ontario based company said it no longer expects to meet its forecast for full-year adjusted diluted earnings of $5.25 to $6.00 a share.

Nasdaq-listed shares of RIM have fallen roughly 65 percent this year as Apple's iPhone and Google's Android devices eat up its market share in the smartphone market.

RIM was late to the game with its PlayBook, introducing the tablet last April, long after Apple's iPad had established its dominance of the new segment.

Aiming to drive up lagging PlayBook sales, RIM last month began to offer all versions of the tablet at significantly marked down prices.

RIM is continuing to suffer from its Playbook endeavors. It hurt RIM initially by diverting focus but muted demand is now becoming clearly visible in the financials, said Geoff Blaber, analyst at CCS Insight.

RIM said the $360 million charge in the quarter reflects the current market environment and allows it to expand upon the aggressive level of promotional activity recently employed.

The company, which will report its quarterly results on December 15, said the promotion will help boost PlayBook sales and help it reduce its inventories.

RIM is committed to the BlackBerry PlayBook, said Co-Chief Executive Mike Lazaridis. Early results from recent PlayBook promotions indicate a significant increase in demand across most channels.

(Reporting by Euan Rocha; Editing by Frank McGurty)