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Published byMelina Sherman Modified over 9 years ago
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D ATA A CQUISITION AND M ANIPULATION
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A NALOG V S. D IGITAL Q UANTITIES 2
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E LEMENTS OF A D ATA A CQUISITION S YSTEM 3
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S IGNAL D IGITIZATION
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A LIASING E FFECTS 5
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S AMPLE AND H OLD 6
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S AMPLE AND H OLD C HARACTERISTICS 7
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A/D C ONVERSION B ASICS 8
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A/D R ESOLUTION AND Q UANTIZATION E RROR 9
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Q UANTIZATION E RROR 10
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16F877 A/D C ONVERTER 11
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A NALOGUE I NPUT M ODEL 12
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T IMING R EQUIREMENTS FOR O NE A/D C ONVERSION 15
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A/D C ONVERSION S TEPS 1. Configure the A/D module: Configure analog pins/voltage reference and digital I/O (ADCON1) Select A/D input channel (ADCON0) Select A/D conversion clock (ADCON0) Turn on A/D module (ADCON0) 2. Configure A/D interrupt (if desired): Clear ADIF bit Set ADIE bit Set PEIE bit Set GIE bit 3. Wait the required acquisition time. 4. Start conversion: Set GO/DONE bit (ADCON0) 5. Wait for A/D conversion to complete, by either: Polling for the GO/DONE bit to be cleared (with interrupts enabled); OR Waiting for the A/D interrupt 6. Read A/D result register pair (ADRESH:ADRESL), clear bit ADIF, if required. 7. For the next conversion, go to step 1 or step 2, as required. The A/D conversion time per bit is defined as TAD. 16
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A CQUISITION T IME 17
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A/D C ONVERSION C LOCK The A/D conversion time per bit is defined as TAD. The A/D conversion requires a minimum 12TAD per 10- bit conversion. The source of the A/D conversion clock is software selected. TAD must be selected to ensure a minimum TAD time of 1.6 µs. 18
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A/D CONVERSION TAD CYCLES 20
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A/D R ESULT R EGISTERS 21
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R EGISTERS A SSOCIATED WITH A/D 22
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