
1991 Advanced Micro Devices, Inc.
1
Publication #
Rev. Amendment
Issue Date
15923
A
/0
6/91
FDDI on Copper with AMD PHY Components
by Eugen Gershon
INTRODUCTION
This application note outlines an implementation using
AMD PHY components found in either the SUPERNET
1 or SUPERNET 2 families to drive and receive signals
over shielded twisted pair media. The circuit described
meets the electrical specification of the interoperable
solution (PID 16011A) endorsed by AMD, Chipcom,
DEC, Motorola, and SynOptics. This interoperable solu-
tion (IOS) is designed to minimize the cost of FDDI con-
nections confined within 100 meter range by replacing
the optical transceiver and fiber with a shielded twisted
pair (STP) transceiver and STP cabling. If a design util-
izes AMD’s SUPERNET 1 or SUPERNET 2 chipsets, no
major changes are required; only a simple interface cir-
cuit from the PHY transmitter to the cable and another
interface from the cable to the PHY receiver are neces-
sary. The interface can be implemented at minimal cost
and with no more board space requirements than avail-
able optical Media Interface Connectors (MICs). We
built the circuit described herein using surface mount
devices on a small daughter board that was form factor
and pin-out compatible with the MIC device found on
one of our demonstration platforms.
When optical PMD devices are removed from the board,
the signals at their interface to the system should be
kept intact, both in logical content and as voltage/current
levels – see Figure 1. The optical transmitter accepts
both “Serial Data Out” from the PHY transmitter and
“Output Disable” control (not used in IOS), at P-ECL lev-
els. Similarly, the optical receiver supplies “Serial Data
In” to the PHY receiver and “Carrier Detect” status (here
called “Link Detect”) at the same P-ECL levels. One new
signal handled by the copper interface circuit is a status
signal, incorporated into Link Detect, that shows that the
cable is connected at both ends. It is detected by both
transmitter and receiver because each one uses a sepa-
rate twisted pair.
This solution is designed to work on STP cable,
150 ohm, Type 1 or 2. It specifies a maximum FDDI sig-
nal attenuation of 12 dB (a factor of 4) at 100 meters.
Link Detect
PHY
Transmitter
“T”
Copper
Interface
STP
Z0 = 150
Connection Detected
Serial
Data
Out
Connection Detected
Sufficient Power Level
(”Signal Detect”)
AND
D
A
T
A
I
N
PHY
Receiver
“R”
Copper
Interface
STP
Z0 = 150
Serial
Data
In
D
A
T
A
O
U
T
15923A-001A
Figure 1. Block Diagram