PXS20RM Datasheet, PDF (196/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

Analog-to-Digital Converter (ADC)
If the content of all the normal conversion mask registers is zero (that is, no channel is selected) the
conversion operation is considered completed and the interrupt ECH (see Section 9.4.8, Interrupts) is
immediately issued after the start of conversion.
9.4.2.3 Normal conversion operating modes
Two operating modes are available for the normal conversion:
• One Shot
• Scan
To enter one of these modes, you must program the MCR[MODE] bit. The first phase of the conversion
process involves sampling the analog channel and the next phase involves the conversion phase when the
sampled analog value is converted to digital as shown in Figure 9-44.
Sample B Evaluate B Sample C Evaluate C Sample D Evaluate D Sample E Evaluate E
Figure 9-44. Normal conversion flow
In One Shot Mode (MCR[MODE] = 0) a sequential conversion specified in the NCMRs is performed only
once. At the end of each conversion, the digital result of the conversion is stored in the corresponding data
register.
Example 9-1. One Shot Mode (MCR[MODE] = 0)
Channels A-B-C-D-E-F-G-H are present in the device where channels B-D-E are to be converted
in the One Shot Mode. MCR[MODE] = 0 is set for One Shot mode. Conversion starts from the
channel B followed by conversion of channels D-E. At the end of conversion of channel E the
scanning of channels stops.
The MSR[NSTART] status bit is automatically set when the normal conversion starts. At the same time
the MCR[NSTART] bit cleared, allowing the software to program a new start of conversion. In that case
the new requested conversion starts after the running conversion is completed.
In Scan Mode (MODE = 1), a sequential conversion of N channels specified in the NCMRs is
continuously performed. As in the previous case, at the end of each conversion the digital result of the
conversion is stored in the corresponding data register.
The MSR[NSTART] status bit is automatically set when the normal conversion starts. Unlike One Shot
Mode, the MCR[NSTART] bit is not cleared. It can be cleared by software when the user needs to stop
scan mode. In that case, the ADC completes the current scan conversion and, after the last conversion, also
clears the MSR[NSTART] bit.
Example 9-2. Scan Mode (MCR[MODE] = 1)
Channels A-B-C-D-E-F-G-H are present in the device where channels B-D-E are to be converted
in the Scan Mode. MCR[MODE] = 1 is set for Scan Mode. Conversion starts from the channel B
followed by conversion of the channels D-E. At the end of conversion of channel E the scanning
9-38
PXS20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor