G&L MMC-A2, Hardware Manual

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Installation, Operation, & Maintenance
22 MMC Hardware Manual G & L Motion Control Inc.
for high-frequency welders and for pulse-width-modulated motor
drives.
3.5.2 Differential Devices for Analog and Encoder
Signals
A differential device receives or sends one signal over two wires
(typically a shielded twisted pair). The input/output voltage at the
second terminal is the inverse of the first. Information is received/
sent as the difference between the two voltages.
Figure 3-7: Differential Digital Pulse Train
The advantages of using differential signals are:
• A differential signal is less susceptible to electromagnetic
noise. Static or other interference affects both of the twisted-
pair wires equally, so the difference between the normal and
inverted voltage remains unchanged. A differential signal
can be transmitted over a much longer distance or in a much
noisier environment than a single-ended one.
• MMC hardware circuitry can detect signal loss from an
encoder if the signal is differential. The application program
can be set to shut down the application if such an error is
detected.
WARNING
Use care when wiring I/O devices to the MMC and when
plugging in cables. Wiring the wrong device to the con-
nector or plugging a connector into the wrong location
could cause intermittent or incorrect machine operation.
IMPORTANT
Always use differential drivers with differential inputs.
SIGNAL AT A
INVERTED
SIGNAL AT A
DIFFERENTIAL