RE: standard loads on 66 MHz PCI

Greg Edlund asked:

> How new are these Tval loads? Version 2.2 (currently in draft, dated
> June
> 1998)?

Much older than that. They became official at least as early as June
11, 1995, and were available in preliminary form a year before that.
See Version 2.1, note 2 under Table 4-6, on page 134; and Figures 7-6,
7-7, and 7-8 on pages 227-228. Parts for the 5V PCI signaling
environment use the two simple "lumped" test loads (0pF and 50pF), as
these were already in place and in use for Version 2.0 (1993).

Arpad Myranyi said:

> The test load (and waveform) doesn't match the driver's real load
> (and waveform) ...

But I think they do! They are more realistic than the conventional 50pF
lumped test load.

The minimum load represents the limiting case of two PCI devices on a
motherboard with no expansion slots and short etch; a strictly local
bus.

The maximum load represents that first nanosecond or so on a long bus,
before the incident edge bounces off the open ends and returns to the
driver. The waveform you get is ... well ... it's what you really get!

Regards,
Andy Ingraham
Received on Tue Nov 10 05:02:01 1998