hardware fixes

Use of FC-Celeron in Socket370

© www.theregister.co.uk by Diego von Deschwanden

When Intel launched the FC-PGA, we all asked ourselves if our present Socket 370 motherboards with PPGA Celerons would support the flip-chip Coppermine processor. A few points of compatibility are to be taken into consideration: physical, voltage, pinout, and Bios support.

Page at the Intel site that explains Motherboard Compatibility
This paragraph is very interesting: "Current motherboards designed for Intel® Celeron™ processors in the 370-pin socket Legacy motherboards designed for the 370-pin socket will not support the Pentium III processor in the FC-PGA form factor. Pentium III processors in the FC-PGA have two RESET pins, and require VRM 8.4 specifications. The existing motherboards are referred to as Legacy motherboard, and the newer motherboards supporting the second RESET pin and VRM 8.4 are referred to as flexible motherboards. Contact your PC manufacturer for motherboard information"
What is important: VRM 8.4 specification and the two RESET pins.

VRM 8.4
The PIII Coppermine processors use 1.60 to 1.65 core voltage. These voltages are already selectable in a lot of recent motherboards, especially the Abit ones, wich you can select in Bios manually (voltages from 1.30 to 2.05+ are supported). So core voltage shouldn't be an incompatibility issue.

Two RESET pins
Further statements are made in these public (free, available) Intel documents:
Pinout and RESET information for Pentium® IIIE Processors at 500 & 550MHz in PGA370 Socket
datasheet 245264
datasheet 245264 Rev. 01
Pinout and RESET information for Celeron® Processors in FCPGA / PGA370 Socket
datasheet 243658
datasheet 243658 Rev. 09
Closely looking at the pinout of PIII FC-PGA compared to the PPGA Celeron, we can notice that they have the same pinout except for two pins:

pin X4 reserved RESET#

As you see the RESET# pin has moved from AH4 to X4. The RESET# pin is essential to the processor, it wouldn't boot at all if it was not supplied. So suppose you wanted to use a Celeron in a Coppermine motherboard, the RESET# pin has changed, how can a Celeron be supported?
Datasheet 245264, page 46: "RESET# signal must be connected to pins AH4 and X4 for backwards compatibility. Refer to the platform design guide and Section 7.1 for implementation details. If backwards compatibility is not required, then RESET2# (X4) should be connected to GND." It is clear that if a Celeron is inserted, the AH4 and X4 must be connected so the Celeron can have access to the RESET# supply. Also it is obvious that if the board is to be used with PIII FC-PGA processors only, then this connection is not needed. I would like to bring your attention on the fact that Slot 1 (now called SC242) Coppermine PIII's do not have this RESET2# implemented…
So let's see what this new RESET2# pin is about: Read Datasheet 245264, page 68: "RESET2# The RESET2# pin is provided for compatibility with other Intel Architecture processors. The Pentium III processor does not use the RESET2# pin. Refer to the platform design guide for the proper connections of this signal."

So the RESET2# is not used !

This is where you say: "Hey! Wait a minute!" Not only the RESET2# is not used, but also the only functional and important pin has been moved. Intel is tricking us badly! Obviously Intel wants us to buy i810, i820,etc motherboards. Of course, it is all not about pins and voltage. There may be other minor timing and voltage incompatibilities. Only testing will tell.

Diego von Deschwanden