Technical data

1.6.3 100BASE-FX Circuitry
In case of 100BASE-FX operation a standard optical transceiver module (like Agilent HFBR-5803) is
connected to the P(2:1)RDxN, P(2:1)RDxP, P(2:1)SDxN, P(2:1)SDxP, P(2:1)TDxN and P(2:1)TDxP pins.
The connection is straight forward and consists mainly of pull-up and pull-down resistors. The signals
between the PHYs and the transceiver module(s) are 100
Ω differential respectively 50 Ω single-ended
signals. This must be taken into account during PCB design. The external resistors should be placed as
close to the ERTEC 200 pins as possible. Figure 10 shows the details of the circuit.
Figure 10: 100BASE-FX Interface Example
Note: The circuitry in the transmit path deviates slightly from the examples that are typically given in
optical transceiver data sheets. However it is required to implement the circuit above in order to
provide pECL-compliant output levels.
In applications that do not use 10BASE-T respectively 100BASE-TX modes, but only the 100BASE-FX
mode, the analog I/Os P(2:1)TxN, P(2:1)TxP, P(2:1)RxN and P(2:1)RxP should be left open. Only
EXTRES must still be connected with the 12.4 k
Ω resistor to analog GND.
82 Ω
150 Ω
150 Ω
VDD
GND
ERTEC 200
P(2:1)RDxP
P(2:1)RDxN
P(2:1)TDxN
P(2:1)TDxP
Optical
transceiver
All resistors: 1/8 W and 1% tolerance
VRef: VDD (PECL) - 1.3 V
140 Ω
140 Ω82 Ω
130 Ω
130 Ω 82 Ω
82 Ω
P(2:1)SDxP
P(2:1)SDxN
130 Ω 82 Ω
TD
RD
SD
TD
RD
VRef
Copyright © Siemens AG 2008. All rights reserved. Page 56 ERTEC 200 PHY
Technical data subject to change Version 1.0.0