ATTiny 85 divide a 16 bit number by two

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badbaud
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Posted by badbaud: Fri. Jan 27, 2012 - 09:39 AM
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Code written in assembly, no C.

LSR is a 8 bit function, is there any code available that shows how to use the LSR function to shift an entire 16 bit word to the right by two?

BADBAUD

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AVR Microcontrollers, megaAVR and tinyAVR
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Kartman
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Posted by Kartman: Fri. Jan 27, 2012 - 09:48 AM
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Use the carry bit. Clear carry first. Do the shift on the high byte and the carry has the bit that dropped out then shift the low byte. Job done.

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MBedder
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Posted by MBedder: Fri. Jan 27, 2012 - 10:13 AM
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No need to clear the carry bit first:

        lsr     r17     ; Shift MSB, MSB.7 resets, MSB.0 goes to CY
        ror     r16     ; Rotate LSB, CY goes to LSB.7

Job done :)

Warning: Grumpy Old Chuff. Reading this post may severely damage your mental health.

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badbaud
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Posted by badbaud: Sat. Jan 28, 2012 - 05:49 AM
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Thanks, then I just repeat that twice to divide a 16 bit number by two.

BADBAUD

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MBedder
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Posted by MBedder: Sat. Jan 28, 2012 - 07:04 AM
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No you don't. The code above does this alone.

Warning: Grumpy Old Chuff. Reading this post may severely damage your mental health.

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Bronze Marktheusch
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Posted by theusch: Sat. Jan 28, 2012 - 03:24 PM
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Quote:

is there any code available that shows how to use

Find the AVR app note on "16-Bit Arithmetics".
Quote:

no C.


Going at it blind, eh? :twisted:

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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