
MC68F375
QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE-64
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
5-11
conversion queues as directly connected signals. Software simply puts the channel
number of an externally multiplexed channel into a CCW.
Figure 5-3 shows that MA[2:0] may also be analog or digital input pins. When external
multiplexing is selected, none of the MA[2:0] pins can be used for analog or digital
inputs. They become multiplexed address outputs.
5.8 Analog Input Channels
The number of available analog channels varies, depending on whether or not external
multiplexing is used. A maximum of 16 analog channels are supported by the internal
multiplexing circuitry of the converter. Table 5-2 shows the total number of analog
input channels supported with zero-to-four external multiplexers.
5.9 Analog Subsystem
The QADC64 analog subsystem includes a front-end analog multiplexer, a digital-to-
analog converter (DAC) array, a comparator, and a successive approximation register
(SAR).
The analog subsystem path runs from the input pins through the input multiplexing cir-
cuitry, into the DAC array, and through the analog comparator. The output of the
comparator feeds into the SAR.
Figure 5-4 shows a block diagram of the QADC64 analog submodule.
Table 5-2 Analog Input Channels
Number of Analog Input Channels Available
Directly Connected + External Multiplexed = Total Channels1
NOTES:
1. When external multiplexing is used, three input channels become multiplexed address out-
puts, and for each external multiplexer chip, one input channel becomes a multiplexed ana-
log input.
No External
Mux Chips
One External
Mux Chip
Two External
Mux Chips
Three External
Mux Chips
Four External
Mux Chips
16
12 + 8 = 20
11 + 16 = 27
10 + 24 = 34
9 + 32 = 41
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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