AMD-762 Datasheet, PDF (20/122 Pages) Advanced Micro Devices – System Controller

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