shamino wrote on 2023-07-27, 18:39:The regulator is made to be compatible with the 5-bit VID setting that is provided by later Intel P2/P3 CPUs. It covers the ran […]
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gerwin wrote on 2023-07-27, 17:07:
shamino wrote on 2023-07-27, 16:10:
I looked at the pdf manual there earlier.
The voltage jumpering is a bit primitive. It seem like it starts with 2,0V as a baseline. Then the four jumpers allow for adding 0,1V / 0,2V / 0,4V / 0,8V. Or combinations of these four values. Adding all four makes 2 + 0,1 + 0,2 + 0,4 + 0,8 = 3,5V.
The regulator is made to be compatible with the 5-bit VID setting that is provided by later Intel P2/P3 CPUs. It covers the range from 1.3-3.5V. The jumpers just make that setting manual, since socket-7 CPUs don't have pins for automatic VID.
The way Intel defined the VID values, there is an odd shift in the scheme that happens at 2.0V or 2.05V, so the pattern changes when going above or below that value. There's actually some overlap - there's 2 ways to declare 2.0V but some regulators only allow 1 of them (including this LM2637 - that's why it went to no output with all jumpers removed).
On my super-7, I use a red jumper cap for the high order VID jumper. It serves as a reminder to not move it. This ensures the voltage can't go any higher than 2.05V.
In the picture it looked like there are 5 jumpers. If there are only 4, then it means the high order bit is soldered, so then the minimum will be 2.0V. But if all 5 jumpers are present then it can go below 2.0V.
On my board (different brand/model), early revisions only had 4 jumpers but later revisions added the 5th.
Very nice explanation,
If memory serves, the way some of these work is as follows
The one you call high order basically cuts all values in half.
Goes from 2.0 base voltage (not working) to 1.2 or 1.3v but that isn’t all
The jumpers that were once +0.1, + 0.2, + 0.4, +0.8v become +.05, +0.1, + 0.2, + 0.4
Giving finer precision in the lower range.
So 1.3v plus +.05, 0.1, 0.2, 0.4 equals 2.05 if you remove the .05 you get 2.0.
As you said, two ways to reach 2.0. 😀