MPC555CME Freescale Semiconductor, MPC555CME Datasheet - Page 421

• Manufacturer Part Number: MPC555CME
• Description: KIT EVALUATION FOR MPC555
• Manufacturer: Freescale Semiconductor
• Type: Microcontrollerr

Specifications of MPC555CME

• Contents: Module Board, Installation Guide, Power Supply, Cable, Software and more
• Processor To Be Evaluated: MPC555
• Data Bus Width: 32 bit
• Interface Type: RS-232
• For Use With/related Products: MPC555
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

13.7 External Multiplexing Operation
MPC555
USER’S MANUAL
Since port B is input-only, a data direction register is not needed. Read operations on
the reserved bits in DDRQA return zeros, and writes have no effect. Refer to
Port Data Direction Register
External multiplexers concentrate a number of analog signals onto a few inputs to the
analog converter. This is helpful in applications that need to convert more analog sig-
nals than the A/D converter can normally provide. External multiplexing also puts the
multiplexer closer to the signal source. This minimizes the number of analog signals
that need to be shielded due to the close proximity of noisy, high-speed digital signals
near the MCU.
The QADC64 can use from one to four external multiplexers to expand the number of
analog signals that may be converted. Up to 32 analog channels can be converted
through external multiplexer selection. The externally multiplexed channels are auto-
matically selected from the channel field of the CCW table, the same as internally mul-
tiplexed channels.
All of the automatic queue features are available for externally and internally multi-
plexed channels. The software selects externally multiplexed mode by setting the
MUX bit in QACR0.
Figure 13-3
to the QADC64. The external multiplexers select one of eight analog inputs and con-
nect it to one analog output, which becomes an input to the QADC64. The QADC64
provides three multiplexed address signals (MA[2:0]), to select one of eight inputs.
These outputs are connected to all four multiplexers. The analog output of each mul-
tiplexer is each connected to one of four separate QADC64 inputs — ANw, ANx, ANy,
and ANz.
/
MPC556 QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE-64
Caution should be exercised when mixing digital and analog inputs.
This should be minimized as much as possible. Input pin rise and fall
times should be as large as possible to minimize AC coupling effects.
shows the maximum configuration of four external multiplexers connected
for register and bit descriptions.
Rev. 15 October 2000
MOTOROLA
13.12.5
13-9