MC68HC908GZ8 Datasheet, PDF (67/344 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Analog-to-Digital Converter (ADC)
Functional Description
5.3.3 Conversion Time
Conversion starts after a write to the ADC status and control register (ADSCR).
One conversion will take between 16 and 17 ADC clock cycles. The ADIVx and
ADICLK bits should be set to provide a 1-MHz ADC clock frequency.
Conversion time = ^{16 to 17 ADC cycles}
ADC frequency
Number of bus cycles = conversion time × bus frequency
5.3.4 Conversion
In continuous conversion mode, the ADC data register will be filled with new data
after each conversion. Data from the previous conversion will be overwritten
whether that data has been read or not. Conversions will continue until the ADCO
bit is cleared. The COCO bit is set after each conversion and will stay set until the
next read of the ADC data register.
In single conversion mode, conversion begins with a write to the ADSCR. Only one
conversion occurs between writes to the ADSCR.
When a conversion is in process and the ADCSCR is written, the current
conversion data should be discarded to prevent an incorrect reading.
5.3.5 Accuracy and Precision
The conversion process is monotonic and has no missing codes.
5.3.6 Result Justification
The conversion result may be formatted in four different ways:
1. Left justified
2. Right justified
3. Left Justified sign data mode
4. 8-bit truncation mode
All four of these modes are controlled using MODE0 and MODE1 bits located in
the ADC clock register (ADCLK).
Left justification will place the eight most significant bits (MSB) in the corresponding
ADC data register high, ADRH. This may be useful if the result is to be treated as
an 8-bit result where the two least significant bits (LSB), located in the ADC data
register low, ADRL, can be ignored. However, ADRL must be read after ADRH or
else the interlocking will prevent all new conversions from being stored.
MC68HC908GZ8
MOTOROLA
Analog-to-Digital Converter (ADC)
For More Information On This Product,
Go to: www.freescale.com
Data Sheet
67