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09/16/12 17:22
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#188361 - TIA and ADC clock speed.
Responding to: Richard Erlacher's previous message
Richard and Kai, thanks for the thoughts.
Yes, I realize the conversion clock must be slower. I used every combination with the clock speed bits. Clock is currently at the default 2mhz. The processor is running at 20mhz.
The TIA- also yes. Transimpedence amp AKA current to voltage converter.
I have an LM324 connected as a TIA. The LM324 operates at 3.3V, unlike the TL084 which needs over twice that. I am assuming the LM324 will work in this circuit but don't know for sure. A lot of internet TIA examples use the 324.

My circuit
AT89LP6440 with 3.3V supply.
One led connects to P1.0 for visual.
dac connections: neg to neg, pos to pos (Dac to 324 opamp)
positive connections go to a pot(3.3V to ground) so I can vary that level and easily set it to Vdd/2. Output follows the pot + input.
Feedback resistor- 4.7K to 100K.
software simply increments A, sends it to the msb Dac register(DADH), then a slight delay of $FF clock cycles.
The DAC and ADCE bits are set, as instructed.
I set the go bit (DADC.6) for each conversion with ORL DADC.6.
I have gone over and over Atmels 6440 pdf file, setting the bits as instructed, trying different combinations. Can't see it yet.
Still no output.

List of 4 messages in thread
AT89LP6440 no dac output      Rick Gebhardt      09/15/12 10:58      
   You're aware that this is a differential DAC, right?      Richard Erlacher      09/15/12 17:03      
      TIA and ADC clock speed.      Rick Gebhardt      09/16/12 17:22      
   Have you noticed...      Kai Klaas      09/15/12 17:06      

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