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4M30 Camera User's Manual
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EIA-644 is an electrical specification for the transmission of digital data. The standard is
available from the EIA (Electronic Industries Association). It defines voltage levels,
expected transmission speeds over various cable lengths, common mode voltage
operating requirements for transmitters and receivers, and input impedances and
sensitivities for receivers.
The standard requires that two wires (e.g. twisted pair) be used to transmit one signal in a
differential mode. This means that one wire will be logic HIGH while the other wire is
logic LOW. Voltage swing between HIGH and LOW is approximately 350mV, with a
typical offset of approximately 1.25V. The use of differential signal transmission allows
the receiver to reject common mode voltages. This noise rejection improves data integrity
and allows cameras to be installed in an industrial environment.
EIA-644-compatible line receivers and drivers are available from many different IC
manufacturers in a variety of fabrication technologies such as CMOS and GaAs. The EIA-
644 standard does not define specific voltages, so it can migrate from 5V power supplies
to 3.3V and sub-3V. DALSA recommends the use of 5V CMOS line drivers and receivers
such as National Semiconductor parts DS90C0C31 quad line driver and DS90C032 quad
line receiver.
To achieve full benefit of the common mode rejection, twisted pair cable should be used
for all EIA-644 signals. The cable impedance should be 100 Ohms and the cable
terminated at the receiving end with a 100 Ohm resistor. All EIA-644 inputs in a DALSA
camera are terminated with 100 Ohms between the (+) and (-) of a signal. Figure A-1 (a)
shows an example of an EIA-644 transmission.
DALSA indicates the (+) signal by the name of the signal; i.e. MCLK, while the (-) signal
is indicated by either an overscore over the name or appending the letter B to the end of
the name; i.e.
which is sent or received; i.e. when MCLK in the TTL domain is HIGH then MCLK in the
EIA-644 domain is HIGH. The (-) signal has the opposite sense of the TTL domain signal
and so if MCLK TTL is HIGH then MCLKB EIA-644 is LOW. Figure 9 shows the
relationship.
DALSA
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or MCLKB. The (+) signal has the same sense as the TTL signal
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