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Functional Description
directly connected signals. User software simply puts the channel number of externally
multiplexed channels into CCWs.
Figure 27-18 shows that the two MA signals may also be analog input signals. When
external multiplexing is selected, none of the MA signals can be used for analog or digital
inputs. They become multiplexed address outputs and are unaffected by DDRQA[1:0].
27.7.2.2 Module Version Options
The number of available analog channels varies, depending on whether external
multiplexing is used. A maximum of eight analog channels are supported by the internal
multiplexing circuitry of the converter. Table 27-21 shows the total number of analog input
channels supported with 0 to 4 external multiplexer chips.
No External Mux One External Mux
8
1
The external trigger inputs are not shared with two analog input signals.
2
When external multiplexing is used, two input channels are configured as multiplexed address outputs,
and for each external multiplexer chip, one input channel is a multiplexed analog input.
27.7.3 Analog Subsystem
This section describes the QADC analog subsystem, which includes the front-end analog
multiplexer and analog-to-digital converter.
27.7.3.1 Analog-to-Digital Converter Operation
The analog subsystem consists of the path from the input signals to the A/D converter
block. Signals from the queue control logic are fed to the multiplexer and state machine.
The end-of-conversion (EOC) signal and the successive approximation register (SAR)
reflect the result of the conversion. Figure 27-19 shows a block diagram of the QADC
analog subsystem.
27-34
Table 27-21. Analog Input Channels
Number of Analog Input Channels Available
Directly Connected + External Multiplexed = Total Channels
Two External
5 + 4 = 9
MCF5282 User's Manual
Three External
Muxes
Muxes
4 + 8 = 12
3 + 12 = 15
1, 2
Four External
Muxes
2 + 16 = 18
MOTOROLA
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