MPC555
/
MPC556
QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE-64
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
13-5
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.
13.3.5 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
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 ad-
dress outputs.
13.3.6 Voltage Reference Pins
V
RH
and V
RL
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
filtering, which increases reference voltage precision and stability, and subsequently
contributes to a higher degree of conversion accuracy.
13.3.7 Dedicated Analog Supply Pins
V
DDA
and V
SSA
pins supply power to the analog subsystems of the QADC64 module.
Dedicated power is required to isolate the sensitive analog circuitry from the normal
levels of noise present on the digital power supply.
13.3.8 External Digital Supply Pin
Each port A pin includes a digital output driver, an analog input signal path, and a dig-
ital input synchronizer. The V
SS
pin provides the ground level for the drivers on the port
A pins. V
DDH
provides the supply level for the drivers on port A pins.
13.3.9 Digital Supply Pins
V
DD
and V
SS
provide the power for the digital portions of the QADC64, and for all other
digital MCU modules.
Table 13-1 Multiplexed Analog Input Channels
Multiplexed Analog Input
Channels
ANw
Even-numbered channels from 0 to 14
ANx
Odd-numbered channels from 1 to 15
ANy
Even-numbered channels from 16 to 30
ANz
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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