
MC68F375
QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE-64
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
5-53
AMCHAN[1:0]. Address lines to select between the 4 multiplexers. This selection
appears redundant since the final selection between the 4 multiplexers is done by the
QADC64 module. This redundancy is added to reduce the dynamic charging current
required from the input pin. These pins perform a disable function more than a select
function. Only 1 of the 4 multiplexers can be active at a time. These address lines dis-
able the other 3 multiplexers so that none of their switches are closed. As the selected
multiplexer cycles through its various inputs, the other multiplexers draw no dynamic
charging current through their inputs. Without this disable function (as in the external
multiplexer case), pins on all 4 multiplexers would draw current even though only 1
multiplexer would actually be in use.
Assuming that AMCHAN[1:0] change simultaneously with AMMA[2:0], break before
make switching ensures that on each channel change the following occurs:
1. All 4 multiplexers are disabled
2. The desired input ANX0-15 is selected
3. The appropriate multiplexer is enabled
AMPMUX. When low this signal disables all multiplexer inputs. It is used in conjunction
with AMCHAN[1:0] to reduce dynamic charging current into the AMUX analog pins.
This signal is normally low when the direct inputs to the QADC64 are selected.
AMADB[1:0]. The 2 multiplexer outputs from the AMUX.
Table 5-22 AMUX I/O Functionality
AMPMUX
AMCHAN[1:0]
AMMA[2:0]
AMADB3
AMADB2
AMADB1
AMADB0
0
XX
XXX
Z
1
00
000
Z
ANX0
1
00
001
Z
ANX2
1
00
010
Z
ANX4
1
00
011
Z
ANX6
1
00
100
Z
ANX8
1
00
101
Z
ANX10
1
00
110
Z
ANX12
1
00
111
Z
ANX14
1
01
000
Z
ANX1
Z
1
01
001
Z
ANX3
Z
1
01
010
Z
ANX5
Z
1
01
011
Z
ANX7
Z
1
01
100
Z
ANX9
Z
1
01
101
Z
ANX11
Z
1
01
110
Z
ANX13
Z
1
01
111
Z
ANX15
Z
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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