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The EM203 has two connectors -- main connector and magnetics connector. Depending on the EM203 version, magnetics connector can be soldered facing up or down, as described in the Mechanical Dimensions topic.

Main connector
#1
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MD*
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Input
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Mode selection pin
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#2
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RST
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Input
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Reset, active high
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#3
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P3
DTR*
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Input/output
Output
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General-purpose input/output line
Data terminal ready output
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#4
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P2
DSR*
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Input/output
Input
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General-purpose input/output line
Data set ready input
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#5
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L3
SG*
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Output
Output
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LED output 3
Green status LED control line
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#6
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L4
SR*
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Output
Output
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LED output 4
Red status LED control line
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#7
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VCC
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Positive power input, 5V nominal, +/- 5%, app. 220mA
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#8
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GND
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Ground
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#9
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RX
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Input
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Serial receive line
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#10
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TX
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Output
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Serial transmit line
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#11
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P4
CTS/SEL*
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Input/output
Input
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General-purpose input/output line
Clear to send input; full-/half-duplex selection input
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#12
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P5
RTS/DIR*
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Input/output
Output
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General-purpose input/output line
Request to send output (full-duplex mode); data direction control output (half-duplex mode)
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* Implemented in (supported through) firmware.
Magnetics connector
#1
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RX+
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Input
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Ethernet port, positive line of the differential input signal pair
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#2
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RX-
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Input
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Ethernet port, negative line of the differential input signal pair
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#3
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AVCC
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Output
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"Clean" 1.8V power output for magnetics circuitry
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#4
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---
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---
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---
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#5
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---
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---
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---
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#6
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GND
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Ground
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#7
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TX+
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Output
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Ethernet port, positive line of the differential output signal pair
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#8
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TX-
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Output
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Ethernet port, negative line of the differential output signal pair
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