Motorola MCF5282 Analog Subsystem, Module Version Options, Analog-to-Digital Converter Operation

Models: MCF5282 MCF5281

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Functional Description

directly connected signals. User software simply puts the channel number of externally multiplexed channels into CCWs.

Figure 27-18shows 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].

27.7.2.2Module 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 27-21shows the total number of analog input channels supported with 0 to 4 external multiplexer chips.

Table 27-21. Analog Input Channels

Number of Analog Input Channels Available

Directly Connected + External Multiplexed = Total Channels 1, 2

No External Mux

One External Mux

Two External

Three External

Four External

Muxes

Muxes

Muxes

 

 

 

 

 

 

 

8

5 + 4 = 9

4 + 8 = 12

3 + 12 = 15

2 + 16 = 18

 

 

 

 

 

1The external trigger inputs are not shared with two analog input signals.

2When 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.

27.7.3Analog Subsystem

This section describes the QADC analog subsystem, which includes the front-end analog multiplexer and analog-to-digital converter.

27.7.3.1Analog-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 27-19shows a block diagram of the QADC analog subsystem.

27-34

MCF5282 User’s Manual

MOTOROLA

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Motorola MCF5282 Analog Subsystem, Module Version Options, Analog-to-Digital Converter Operation, Analog Input Channels