Asynchronous operation on timer2

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firmware
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Joined: Tue. Jun 5, 2007
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Posted by firmware: Wed. Jan 30, 2008 - 01:51 PM
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Hi all,

I'm trying to make the RTC on ATMEGA48 by using timer/counter2 in asynchronous operation mode by base on AVR134 application note, but no counting start on timer/counter2 after simulated with AVR Studio. Could any body suggest me the wrong point on my code ?

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File rtc.c

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AVR Microcontrollers, megaAVR and tinyAVR
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clawson
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Location: (using avr-gcc in) Finchingfield, Essex, England
Posted by clawson: Wed. Jan 30, 2008 - 01:58 PM
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This may seem like an awfully silly question but you have connected an external 32768Hz crystal across the TOSC1/TOSC2 pins haven't you?

(To be honest I didn't realise that the simulator was able to simulate that - so not sure how you can have verified it there?)

EDIT: in fact (from the simulator manual):

Quote:
Timer/Counters
16-bit Timer/Counters on all devices have several problems with PWM, prescaler and output compare. Output compare registers are not buffered properly.

The Asynchronous Status Register (ASSR) is not supported in timers with asynchronous mode. This is due to lack of a generic external clock implementation

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