SD39EAM-1r4 Circuit Description
September 2005 4-3
Power is normally supplied to each isolated channel via an isolation power transformer driven by a power
chopper DC-to-DC converter circuit. The transformer secondary’s voltage waveform is AC coupled into
the ASIC’s clock input in addition to being rectified for isolated 24 Vdc ASIC and I/O power. The 24
Vdc I/O field power is switched through an opto-coupler and applied through a diode to the PWR
terminal on a local or remote termination assembly. Additionally, the 24 Vdc is connected by a diode to
the O-Sense pin of the ASIC. This pin is used for diagnosing the condition of the 24 Vdc supply and
detecting the state of the external opto-coupler.
The ASIC features the following:
• An ADC (Analog-to-Digital Converter) for input signals of 0-5V or 0-20mA
• A DAC (Digital-to-Analog Converter) for an output signal of 0-20 mA
• Reads voltage or current frequency inputs at frequencies up to 46080 Hz
• Contains built-in diagnostics
• Designed for bi-directional Manchester encoded serial data over a communications transformer for
ease of isolation
• Uses HDLC (Hi-Level Data Link Control) protocol
• Synchronous internal digital circuits are clocked by an external clock derived from the power
transformer secondary
Each EAM channel can be separately configured via APACS 4-mation configuration software to be one
of the following channel types:
• Analog input (4-20mA, 0-20mA, 1-5V, or 0-5V)
• Analog output (4-20mA or 0-20mA)
• Frequency input (0-46 kHz)
• Totalizer input
• Discrete input (sinking or sourcing)
• Discrete output (sourcing)
An EAM configuration is downloaded into the module’s memory and a copy of the configuration is
stored in the associated control module’s non-volatile memory.
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