MC68HC908LJ24 Datasheet, PDF (338/464 Pages) Motorola, Inc – Microcontrollers

Analog-to-Digital Converter (ADC)
16.4.4 Continuous Conversion
In the continuous conversion mode, the ADC continuously converts the
selected channel, filling the ADC data register (ADRH:ADRL) 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 can be cleared by writing to the ADC status and control
register or reading of the ADRL data register.
16.4.5 Result Justification
The conversion result may be formatted in four different ways.
• Left justified
• Right justified
• Left justified sign data mode
• 8-bit truncation
All four of these modes are controlled using MODE0 and MODE1 bits
located in the ADC clock control register (ADCLK).
Left justification will place the eight most significant bits (MSB) in the
ADC data register high (ADRH). This may be useful if the result is to be
treated as an 8-bit result where the least significant two bits, 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.
Right justification will place only the two MSBs in the corresponding ADC
data register high (ADRH) and the eight LSB bits in ADC data register
low (ADRL). This mode of operation typically is used when a 10-bit
unsigned result is desired.
Left justified sign data mode is similar to left justified mode with one
exception. The MSB of the 10-bit result, AD9 located in ADRH is
complemented. This mode of operation is useful when a result,
represented as a signed magnitude from mid-scale, is needed.
Data Sheet
338
Analog-to-Digital Converter (ADC)
MC68HC908LJ24/LK24 — Rev. 2.1
Freescale Semiconductor