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AMD-762

AMD-762™ System Controller

Advanced Micro Devices 

Preliminary Information

AMD-762™ System Controller Data Sheet

24416C—December 2001

2.1.2

2.1.3

8

Point-to-Point, Source Synchronized

All of the AMD Athlon system bus signals use a terminated,

point-to-point topology—that is, there is one signal connection

plus termination on each end of each wire. The terminated

point-to-point topology allows the use of incident wave

signalling, eliminating most of the time for transmission line

reflections. This feature allows high-transfer speeds while

maintaining high signal integrity. All data transfer is

synchronized by a clock generated at the data source. The clock

and data propagate over matched length paths, minimizing

skew between clock and data, and the data is sampled at the

destination using this forwarded clock.

Data is sampled into a FIFO at the receiver synchronous to the

forwarded clock and read out of FIFO a programmable number

of processor clocks later, reducing all metastability concerns.

The initialization procedure establishes the location of a

common ClockN on both ends of the wire to within the system

wide, clock distribution skew. A data object, transmitted from

one end of the wire on ClockM, is sampled into the FIFO at the

other end of the wire by ClockM forwarded with the data. It is

read from the FIFO by ClockM+X that is generated in the

receivers clock domain, X clocks later. X is a programmed

constant that accounts for the worst case propagation delay.

A detailed description of the AMD Athlon system bus,

including operations, initialization, and timing can be found in

the AMD Athlon™ System Bus Specification, order# 21902, and

the AMD Athlon™ System Bus Design Guide, order# 22666.

Push-Pull Compensation

The AMD-762 system controller provides push-pull driver

configuration. The push-pull driver scheme implements drivers

with a user-defined output impedance. This feature allows the

point-to-point signals to be source terminated without any

external devices, greatly simplifying layout and reducing cost.

In current semiconductor technology, it is not possible to

implement a transistor with a tightly controlled impedance

over realistic voltage, temperature, and process parameters.

For this reason, a dynamic compensation scheme is

implemented. For a push-pull transmission line example, see

Figure 3 on page 9.

Functional Operation

Chapter 2

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