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| Errata (All Date Codes): Missed Watchdog Timer Reset Problem There is a synchronization problem between the watchdog clock and the AVR(R) clock. Even though the clock inputs to both the watchdog timer and the AVR core are generated through the same crystal, the two clock sources are not going through the same PLL. The AVR is clocked at 12 MHz and the watchdog timer is clocked at 1MHz. The WDR (Watchdog Reset) instruction is a one-clock-cycle instruction. As such, when a watchdog timer reset occurs due to a WDR, the watchdog timer may miss the reset. This happens frequently if the AVR is clocked much faster than the watchdog timer. Fix/Workaround A workaround is to invoke the WDR repetitively to ensure that the watchdog timer will be able to receive the reset signal. If the AVR runs at 12 MHz, the WDR command must be invoked fourteen times back to back. The following is the sample code for resetting and arming the watchdog timer, assuming the AVR is running at 12 MHz: asm ( "ldi r16,15\n WDR\n WDR\n WDR\n WDR\n WDR\n WDR\n WDR\n WDR\n WDR\n WDR\n WDR\n WDR\n WDR\n out 0x21,r16 " ); USB Microcontrollers To disarm and disable the watchdog, do the following: asm ( "ldi r16,0x18\nldi r17,0x10\n\n out 0x21,r16\n out 0x21,r17 " ); AT43USB320A AT43USB325 AT43USB326 AT43USB351M AT43USB353M AT43USB355 Errata Sheet Please note that if the AVR runs at 24 MHz, the WDR should be invoked twenty-six times. 3469A-USB-4/04 Atmel Corporation 2325 Orchard Parkway San Jose, CA 95131, USA Tel: 1(408) 441-0311 Fax: 1(408) 487-2600 Atmel Operations Memory 2325 Orchard Parkway San Jose, CA 95131, USA Tel: 1(408) 441-0311 Fax: 1(408) 436-4314 RF/Automotive Theresienstrasse 2 Postfach 3535 74025 Heilbronn, Germany Tel: (49) 71-31-67-0 Fax: (49) 71-31-67-2340 1150 East Cheyenne Mtn. Blvd. Colorado Springs, CO 80906, USA Tel: 1(719) 576-3300 Fax: 1(719) 540-1759 Regional Headquarters Europe Atmel Sarl Route des Arsenaux 41 Case Postale 80 CH-1705 Fribourg Switzerland Tel: (41) 26-426-5555 Fax: (41) 26-426-5500 Microcontrollers 2325 Orchard Parkway San Jose, CA 95131, USA Tel: 1(408) 441-0311 Fax: 1(408) 436-4314 La Chantrerie BP 70602 44306 Nantes Cedex 3, France Tel: (33) 2-40-18-18-18 Fax: (33) 2-40-18-19-60 Biometrics/Imaging/Hi-Rel MPU/ High Speed Converters/RF Datacom Avenue de Rochepleine BP 123 38521 Saint-Egreve Cedex, France Tel: (33) 4-76-58-30-00 Fax: (33) 4-76-58-34-80 Asia Room 1219 Chinachem Golden Plaza 77 Mody Road Tsimshatsui East Kowloon Hong Kong Tel: (852) 2721-9778 Fax: (852) 2722-1369 ASIC/ASSP/Smart Cards Zone Industrielle 13106 Rousset Cedex, France Tel: (33) 4-42-53-60-00 Fax: (33) 4-42-53-60-01 1150 East Cheyenne Mtn. Blvd. Colorado Springs, CO 80906, USA Tel: 1(719) 576-3300 Fax: 1(719) 540-1759 Scottish Enterprise Technology Park Maxwell Building East Kilbride G75 0QR, Scotland Tel: (44) 1355-803-000 Fax: (44) 1355-242-743 Japan 9F, Tonetsu Shinkawa Bldg. 1-24-8 Shinkawa Chuo-ku, Tokyo 104-0033 Japan Tel: (81) 3-3523-3551 Fax: (81) 3-3523-7581 Literature Requests www.atmel.com/literature Disclaimer: Atmel Corporation makes no warranty for the use of its products, other than those expressly contained in the Company's standard warranty which is detailed in Atmel's Terms and Conditions located on the Company's web site. The Company assumes no responsibility for any errors which may appear in this document, reserves the right to change devices or specifications detailed herein at any time without notice, and does not make any commitment to update the information contained herein. No licenses to patents or other intellectual property of Atmel are granted by the Company in connection with the sale of Atmel products, expressly or by implication. Atmel's products are not authorized for use as critical components in life support devices or systems. (c) Atmel Corporation 2004. All rights reserved. Atmel(R) and combinations thereof, and AVR(R) are the registered trademarks of Atmel Corporation or its subsidiaries. Other terms and product names may be the trademarks of others. Printed on recycled paper. 3469A-USB-4/04 |
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