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mdown
Joined: 03 Feb 2006
Location: Dallas, Texas
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Posted: 23 July 2006, 23:36 PM Post subject: 16Mhz? |
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| In a few other boards dealing with Atmega32's I have read about people using 16MHz crystals. Will the ZX-44 operate with a 16MHz crystal? Or should we just stick with a 14.7456 MHz crystal? |
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dkinzer
Site Admin
Joined: 03 Sep 2005
Location: Portland, OR
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Posted: 24 July 2006, 0:19 AM Post subject: |
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The 14.7456MHz crystal was chosen for two reasons. Firstly, and most importantly, that frequency allows reliable serial communication at higher speeds than are attainable when using 16MHz. In particular, the download speed (115.2K baud) is too far off to support reliable communication with a main clock rate of 16MHz. Secondly, the chosen frequency permits greater compatibility with BasicX than could be obtained running at 16MHz.
To answer your specific question, while the chip will run with a 16MHz crystal, the ZBasic VM won't operate correctly. The serial speeds would all be wrong, the RTC would run fast, etc. Virtually all functions that are time-based would be incorrect.
If a faster execution speed is needed for your application a special version of the ZX could be produced. We can discuss this further, if desired, in private email. |
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stevech
Joined: 23 Feb 2006
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Posted: 24 July 2006, 2:39 AM Post subject: |
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| 57600 baud is too far of as well, with 16MHz crystal |
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dkinzer
Site Admin
Joined: 03 Sep 2005
Location: Portland, OR
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Posted: 24 July 2006, 16:18 PM Post subject: |
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| stevech wrote: | | 57600 baud is too far of as well, with 16MHz crystal |
At 1X that is true but setting U2X=1 will yield a speed that is less than 1% off. |
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