MC68F375
QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE-64
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
5-5
5.3.3 External Trigger Input Pins
The QADC64 has two external trigger pins (ETRIG[2:1]). Each of the two external trig-
ger pins is associated with one of the scan queues. When a queue is in external trigger
mode, the corresponding external trigger pin is configured as a digital input.
5.3.4 Multiplexed Address Output Pins
In non-multiplexed mode, the 16 channel pins are connected to an internal multiplexer
which routes the analog signals into the A/D converter.
In externally multiplexed mode, the QADC64 allows automatic channel selection
through up to four external 1-of-8 multiplexer chips. The QADC64 provides a 3-bit mul-
tiplexed address output to the external multiplexer chips to allow selection of one of
eight inputs. The multiplexed address output signals MA[2:0] can be used as multiplex
address output bits or as general-purpose I/O.
When externally multiplexed mode is enabled, MA[2:0] are used as the address inputs
for up to four 1-of-8 multiplexer chips (for example, the MC14051 and the
MC74HC4051). Since MA[2:0] are digital outputs in multiplexed mode, the software
programmed input/output direction and data for these pins in DDQA[2:0], DDRQA, and
PQA[2:0] is ignored, and the value for MA[2:0] is taken from the currently executing
CCW.
5.3.5 Multiplexed Analog Input Pins
In externally multiplexed mode, four of the port B pins are redefined to each represent
a group of eight input channels. Refer to Table 5-1.
The analog output of each external multiplexer chip is connected to one of the AN[w,
x, y, z] inputs in order to convert a channel selected by the MA[2:0] multiplexed
address outputs.
5.3.6 Voltage Reference Pins
VRH and VRL are the dedicated input pins for the high and low reference voltages. Sep-
arating the reference inputs from the power supply pins allows for additional external
Table 5-1 Multiplexed Analog Input Channels
Multiplexed Analog Input
Channels
ANw1
NOTES:
1. If the on-chip multiplexer is enabled, ANw and ANx are used as inputs
for the AMUX outputs.
Even numbered channels from 0 to 14
ANx1
Odd numbered channels from 1 to 15
ANy2
2. If the on-chip AMUX is enabled, then AN2 and AN3 should be read as
channels AN16 and AN17.
Even numbered channels from 16 to 30
ANz2
Odd numbered channels from 17 to 31
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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