AM7968 AMD [Advanced Micro Devices], AM7968 Datasheet - Page 54

• Manufacturer Part Number: AM7968
• Description: TAXIchip Integrated Circuits(Transparent Asynchronous Xmitter-Receiver Interface)
• Manufacturer: AMD [Advanced Micro Devices]

50
1.0 INTRODUCTION
Modern electronic systems move data from point-to-point across physical layer bounda-
ries using either serial or parallel data links. Parallel data links provide fast data
transfers and are compatible with most computer architectures. However, conventional
parallel data links are burdened with cost/performance issues such as costly multi-con-
ductor cables, crosstalk, RFI, bit-to-bit skew and other concerns associated with multiple
wire interfaces. Serial data links, although simpler and less costly, have not provided
sufficient bandwidth to compete with the high data transfer rates of parallel links.
Recent technological advances have altered the cost performance trade-off between
serial and parallel data transfer techniques. A new chip set from Advanced Micro
Devices offers a high performance integrated alternative to traditional serial/parallel data
transfer techniques. The TAXlchip set (Transparent Asynchronous Xmitter-Receiver
Interface) provides the means to establish a transparent high speed serial link between
two high performance parallel buses. The TAXlchip set consists of a Transmitter, which
takes parallel data and transmits it serially at up to 175 MHz, and a Receiver, which
converts the serial data stream back to parallel form. TAXlchips provide a simple parallel
interface through a high speed serial link, while maintaining the data bandwidth required
by the system.
1.1 The Am7968 TAXI Transmitter
The TAXI
register, a multiplying Phase Locked Loop (PLL), and some control logic (Figure 1-1).
Data are input to the latch, encoded, and shifted out at the serial data rate. The encod-
ing used is the efficient 4B/5B scheme specified for the ANSI X3T9.5 Fiber Distributed
Data Interface (FDDI specification). This encoding divides an 8-bit byte into two, 4-bit
nibbles. Each nibble is encoded into a 5-bit symbol. The 10-bit encoded byte is format-
ted into an NRZI data stream for output to the media. This 4B/5B encoding is 80%
efficient, using a 125 Mbaud transmission rate to send 100 Mbps of data.
The Am7968 Transmitter has differential pseudo-ECL (referenced to +5 V) outputs
which can drive 50
shielded twisted pair or coaxial cables.
The pseudo-ECL outputs are also compatible with the ECL interface of optical compo-
nents used to drive fiber optic cable. In addition to providing high bandwidth and low
attenuation, fiber optic data transmission also offers noise immunity, eliminates RFI and
provides data security. Declining optical components costs are bringing the advantages
of fiber optic data transmission to an ever wider range of applications, from process
control to avionics. The TAXlchip set is the ideal complement for fiber optic interfaces.
TAXIchip
Technical Manual
TM
Transmitter consists of an input latch, an encoder, a parallel to serial shift
TM
Integrated Circuits
lines. This capability makes it easy to directly interface with
Publication# 12330
Issue Date: April 1994
Rev. E
Amendment /0