BSEL ??

What in God's name does BSEL stand for? Good question! After reading multiple Intel white papers and asking local voltmod guru, Geoffrey, we now know that BSEL means (host) Bus (speed) Select as in the communication between CPU and PLL clock generator. Depending which pins are held low, or made active, the PLL will build a certain bus clock speed which is directly feed to the CPU.

In any case, by changing the BSEL, you change the default FSB to a higher or lower value. You are in fact changing the strap, mostly done because users want to make a certain chip compatible with a new motherboard. For instance, many people use BSEL mods to make their 133FSB run on a new LGA775 motherboard (which only support FSB200+) or to be able to use more memory dividers when the motherboard has no option to change the strap manually.

Before doing any BSEL modification, make sure that you CPU is capable of running at that FSB at stock voltages as the stock multiplier does NOT change!

Digging in deeper

Let's have a closer look at the Intel white papers, concerning the E6x00 C2D series (.pdf):




Basically, all you need to understand is the table. There are three BSEL 'ports' and two states: High and Low. By switching between high and low, we can change the standard strap to 533, 667 or 800. All other values are "reserved", which means that these do not represent any value. Do not try these reserved values as you might damage you motherboard and your CPU. Via Johnny, we asked Intel about these reserved values, but we received no answer yet.

To get back at the actual BSEL modding, there are two states: high represents voltage and low represents ground, however, it's not that simple. When we're talking about voltage, we mean the Vcc, meaning Voltage Collector to Collector or in human English: the core voltage. The ground in this case is the Vss, Voltage Source to Source. The Vcc voltage can as well be controlled by modifications on the motherboard (or the back of the cpu), but in this case, we don't need this. The way to modify is pretty much the same way as modifying the BSEL, but you have to use the VID[7:0] pins. A table for these processor series can be found on page 17 of the Intel white paper.

Working out the BSEL modifications

Now, how does this work. First of all, you need to locate the BSEL0, BSEL1 and BSEL2 pins, which you can locate by, again, looking in the Intel white papers:



Location:
BSEL0: G29
BSEL1: H30
BSEL2: G30



As you can see, the chip is covered with Vcc and Vss pins, so connecting the BSEL to Vcc or Vss (use a silver inkt pen or maybe solder a switch on you motherboard) should not be a problem. Let's help:

- You want an E6300 to run at 333MHz stock, but it runs at 266MHz stock.
1) BSEL at 266 MHz = L-L-L
2) BSEL at 333 MHz = H-L-L
3) Connect BSEL2 to any Vcc pin

- You want your E4300 to run at 266MHz stock, but it runs at 200MHz stock.
1) BSEL at 200 MHz = L-H-L
2) BSEL at 266 MHz = L-L-L
3) Connect BSEL1 to any Vss pin

Note: Please make sure to check the white paper of your processor type before modifying it. For instance, with my E2160, it would have been impossible to do the BSEL modification (according to the Intel white paper) as all other values, except for the 200MHZ, are reserved. As far as I can see, it might be possible that you could apply the same modifications as the BSEL matches exactly the BSEL for the E6x00 series. However, I did not test did and I don't want you to test it for me. If you do this and succeed, please let me know what you found out.

Update: Apparently all values set for LGA775 processors should be compatible, so one could run his C2D at 400FSB strap without a problem. Just have a look at the other Intel whitepapers or give our forums a visit.

Note #2: Only use straps that are supported by your motherboard. For instance, do not mod to 133FSB if you're using a motherboard that only supports straps of 200FSB and higher.