MMC2107 - Freescale Semiconductor

Freescale Semiconductor, Inc.
Queued Analog-to-Digital Converter (QADC)
Figure 18-18 shows the maximum configuration of four external
multiplexer chips connected to the QADC. The external multiplexer chips
select one of four analog inputs and connect it to one analog output,
which becomes an input to the QADC. The QADC provides two
multiplexed address signals — MA[1:0] — to select one of four inputs.
These inputs are connected to all four external multiplexer chips. The
analog output of the four multiplex chips are each connected to separate
QADC inputs (ANw, ANx, ANy, and ANz) as shown in Figure 18-18.
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Freescale Semiconductor, I
18.9.2.2 Module Version Options
When the external multiplexed mode is selected, the QADC
automatically creates the MA output signals from the channel number in
each CCW. The QADC also converts the proper input channel (ANw,
ANx, ANy, and ANz) by interpreting the CCW channel number. As a
result, up to 16 externally multiplexed channels appear to the conversion
queues as directly connected signals. The software simply puts the
channel number of externally multiplexed channels into CCWs.
Figure 18-18 shows that the two MA signals may also be analog input
pins. When external multiplexing is selected, none of the MA pins can be
used for analog or digital inputs. They become multiplexed address
outputs and are unaffected by DDRQA[1:0].
The number of available analog channels varies, depending on whether
external multiplexing is used. A maximum of 16 analog channels are
supported by the internal multiplexing circuitry of the converter.
Table 18-12 shows the total number of analog input channels supported
with 0 to four external multiplexer chips.
Table 18-12. 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
Muxes
Three External
Muxes
Four External
Muxes
8 5 + 4 = 9 4 + 8 = 12 3 + 12 = 15 2 + 16 = 18
1. The external trigger inputs are not shared with two analog input pins.
2. When external multiplexing is used, two input channels can be configured as multiplexed
address outputs, and for each external multiplexer chip, one input channel is a multiplexed
analog input.
Technical Data MMC2107 – Rev. 2.0
444 Queued Analog-to-Digital Converter (QADC) MOTOROLA
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