AMD-762 Advanced Micro Devices, AMD-762 Datasheet - Page 20

• Manufacturer Part Number: AMD-762
• Description: System Controller
• Manufacturer: Advanced Micro Devices

AMD-762™ System Controller Data Sheet
2.1.2
2.1.3
8
Point-to-Point, Source Synchronized
Push-Pull Compensation
All of the AMD Athlon system bus signals use a terminated,
point-to-point topology—that is, there is one signal connection
plus terminat ion on each end of each wire. The terminated
poin t-to-point topology allows the use of in cid e n t wave
signalling, eliminating most of the time for transmission line
reflections. This fe a tu re allows high-transfer speeds while
ma i n t a i n i n g h i g h s i g n a l i nt e g r i t y. Al l d a t a t ra n s f e r 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.
Th e init ia liza t ion p rocedure e s t ablishes 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
receive rs clock domain, X clocks later. X is a programmed
constant that accounts for the worst case propagation delay.
A d e t a i l e d d e s c r ip t ion o f t he AMD At h l o n s y s t e m b u s,
including operations, initialization, and timing can be found in
the AMDAthlon™ System Bus Specification, order# 21902, and
the AMDAthlon™ System Bus Design Guide, order# 22666.
The AMD-762 system con t roller p rovides push-pull drive r
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 t o
implement a transistor with a tightly controlled impedance
over realistic voltage, temperature, and process parameters.
Fo r t h i s r e a s o n , a d y n a m i c c o m p e n s a t i o n s ch e m e i s
implemented. For a push-pull transmission line example, see
Figure 3 on page 9.
Preliminary Information
Functional Operation
24416C—December 2001
Chapter 2