L12 mod

What is L12 mod and how do i do it? I have an XP 2400+ Tbred B.

There are two logical pins in the Tbred B/Barton CPU called FSB_Sense[0] and FSB_Sense[1] to tell the motherboard that the CPU is originally programmed for FSB 133, or 166, or 200. Details about this and how to alter such are described, for example, in this link. An alternative way to alter such FSB configuration is by physically altering the L12 bridge (I personally prefer the FSB_Sense wiring trick mod than physically opening (burning) or closing (painting) the bridge).

FSB_Sense mod to set Tbred B default FSB from 133 to 166 (page 12)
FSB_Sense mod to set Tbred B default FSB from 133 to 200 (page 12)

Since some ppl reported that by altering the preprogrammed FSB_Sense signals from 133 to 166/200 or vice versa, one could improve the FSB overclocking of ABIT NF7-S rev 2.0 substantially higher (10-15 MHz), that is why the FSB_Sense or L12 mods have been becoming popular. But there are also many found that such mod did not help much at all. I found that the FSB overclocking of the NF7-S rev 2.0 is very tricky, and there is no single recipe would work for all, as detailed in this quote.

hitechjb1 said:

Summary on overclocking the NF7-S rev 2.0 (with Tbred B 1700+ DLT3C and ...)

From my experience on two NF7-S rev 2.0 boards and reading results of many posts, it seems to me that there is no definite combination in terms of the following

- bios version: 10, 14, 16, 18
- L12 mod or FSB_Sense 166/200 mod
- bios setting CPU Interface enable/disable

to achieve highest FSB and memory bandwidth. It has to be tried on a board by board basis (w/ memory modules used) to achieve its max FSB potential, which averaged around 220 MHz, some lower at 210 MHz and some higher to 230 MHz, with stock chipset cooling and without chipset Vdd mod, using good 3200/3500 CAS2 memory with Vdimm at 2.8, 2.9 V if necessary.

I am going to list 6 different situations, no clear trends:

1. Some boards can go to its highest FSB with bios 14, 16, 18, without the L12 and FSB_Sense 166/200 mod (in this situation the mod may help very very little, few MHz (1-3)).

2. Some boards may need the L12 or FSB_Sense 166/200 mod to get stable higher FSB, by as much as 10-15+ MHz.

3. Some boards may need to go back to bios 10 to achieve highest stable FSB. But bios 10 is without the bios fail-safe saving feature of bios 14 or higher. One could get bios corruption w/ bios 10 and need a bios recovery kit to recover.

4. The boards may also require faster CPU above 2.2 GHz to achieve high memory efficiency around 95%.

5. Further, some boards may have stability problem and cannot run at high FSB at certain CPU multipliers (above or below are fine, strange, seeems to be some timing issues ??).

6. Some reported CPU Interface disable made a noticeable higher FSB, as much as 10-15+ MHz. But some can go to highest FSB with or without CPU Interface enabled. But CPU Interface disable has significant negative impact on memory bandwidth performance (6-8%, see below).

It seems to me that the timing of the chipset memory controller, CPU FSB interface, memory modules as a whole making the FSB overclocking very tricky and needed to be done on a case by case basis, without a definite clear recipe.

I think there is an intrinsic limit on FSB based on the combined system timing of the above mentioned components. The board's FSB overclocking would max out at certain level of memory bandwidth (MB/s), regardless of the bios versions, L12 or FSB_Sense mod, CPU Interface, dual channel or single channel, and how well the settings are tweaked and means to achieve the max FSB.

Regardless of the FSB MHz, the number to watch is the effective measured memory bandwidth and memory efficiency, which determine the overall system performance (instead of just FSB MHz). I found that

CPU interface enable (fast decode) and dual channel, integer memory efficiency ~ 95 - 96%

CPU interface disable and dual channel, integer memory efficiency ~ 88-89%

For single channel, memory efficiency would drop by 2-3% but FSB may go few MHz higher, hence single channel and dual channel is roughly a wash on effective memory bandwidth.

Main emphasis for performance should be getting CPU interface enable to work. Since the 6-8% gain of memory efficiency (as described earlier) for memory bandwidth w/ CPU interface enable would be equivalent to 12-18 MHz at the level of 200 MHz FSB. A lower FSB with higher memory efficiency may be better than a higher FSB with lower memory efficiency for both memory bandwidth performance and stability (chipset, memory controller, memory, CPU FSB interface).

Memory bandwidth (MB/s) and memory efficiency can be obtained from the latest Sandra (MAX3) memory bandwidth test, or calculated by

memory_efficiency = measured_memory_bandwidth / (16 x FSB)

Click to expand...

NF7-S rev 2.0 FSB_Sense 166 and 200 mod (from 133) test results (page 12)
NF7-S rev 2.0 FSB_Sense 166 and 200 mod (from 133) test results (part 2) (page 12)

TbredXP 1700 & Abit NF7 rev2.0 boards = Not Very Friendly

NICE, Thanks. I have pc2100 ram though, so it wont be able to run at 166 FSB cause when i try to OC it tops out at 138 FSB. I will need new ram before i do this right?

I don't think the FSB_Sense mod would fix the problem of using slow memory modules to run at too high FSB. One would need PC3200 modules to run at 200 MHz and potentially above.

PC2700 should at least run at 166 MHz on motherboard. If not, it should not be due to CPU. Mostly is the combination of motherboard, PCI bus, multiplier setting, ...

Well i got ****ty memory but will be upgrading soon. I got NF7-s mobo so pci shouldnt be a problem cause it is locked. If i get good ram like pc3500 or pc3700, will makign it go straight to 200 FSB work better?

Constantinos said:

Well i got ****ty memory but will be upgrading soon. I got NF7-s mobo so pci shouldnt be a problem cause it is locked. If i get good ram like pc3500 or pc3700, will makign it go straight to 200 FSB work better?

Click to expand...

I misread you have been using PC2700, and actually you are using PC2100. That is why you are having problem going above 140 MHz. FSB_Sense mod won't help this.

Getting PC3200/3500/3700 should go straight up to 200+. Average about 220 for the NF7-S rev 2.0. Some go to 210 and some to 230 MHz, detailed in my previous post. Good 3200's are cheaper and have good chance to do 220 MHz, and 3500 to 230 MHz.

Well i was gonna get 1 gb buffalo pc3700 BH-5 chips when i get $50 more to afford it. Than i will do 200 FSB mod. Will i need a vdd mod for my NB and a v mem mod for memory? I aiming for 220+ FSB.

Constantinos said:

Well i was gonna get 1 gb buffalo pc3700 BH-5 chips when i get $50 more to afford it. Than i will do 200 FSB mod. Will i need a vdd mod for my NB and a v mem mod for memory? I aiming for 220+ FSB.

Click to expand...

With good memory like you are getting, 220 MHz is the norm for the NF7-S rev 2.0 FSB overclocking. Most likely the Vdd and Vmem from the bios setting suffice. But only actual testing would tell for sure.

Would either of those benefit me with my 1700 Tbred and Nf7-s and mushking lvl II 3200?