Chapter 23 Analog-to-Digital Converter (ADC)
MPC5602P Microcontroller Reference Manual, Rev. 4
582
Freescale Semiconductor
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 interrupt controller chapter for
further details) is immediately issued after the start of conversion.
23.3.1.3
Normal conversion operating modes
Two operating modes are available for the normal conversion:
•
One Shot
•
Scan
To enter one of these modes, it is necessary to 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 23-2. Normal conversion flow
In
One Shot Mode
(MODE = 0) a sequential conversion specified in the NCMR registers is performed
only once. At the end of each conversion, the digital result of the conversion is stored in the corresponding
data register.
Example 23-1. One Shot Mode (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. 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 NSTART status bit in the MSR is automatically set when the Normal conversion starts. At the same
time the MCR[NSTART] bit is reset, 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 NCMR registers is
continuously performed. As in the previous case, at the end of each conversion the digital result of the
conversion is stored into 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 reset. It can be reset 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
resets the MSR[NSTART] bit.
Example 23-2. Scan Mode (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. 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 of channel
Sample B
Convert B
Sample C
Sample D
Convert D
Sample E
Convert E
Convert C