Author Topic: SPI rom Clear CMOS how does it actually work?  (Read 1080 times)

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Offline ESXiTopic starter

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SPI rom Clear CMOS how does it actually work?
« on: April 13, 2020, 09:50:37 pm »
Hi,

I'm modding a board. But it's a laptop so there's no like clear cmos button. So when I make a mistake and need to reset I need to reprogram the bios. I can see some traces to PCH ( could be mistaken).
How does it actually work? Does it send a serial command to the soic 8 and it clears cmos or what happens in the background. By the way it's a MX25L32xxX (mx25l3205dm2i 4mb). Checked the datasheet but don't really understand how it works, still.

Removing battery for 10mins or longer doesn't work by the way. Goal is to reset to default bios nvram.

Any ideas?
my elcheapo lab:
Hantek DSO5102P, KSGER T12 STM32 V2.1S + safety mods, RD6018W DC variable power supply, Quick 861DW, Quick 201B, Telequipment D1011, Optika ST-50LED (ringlight modded)
 

Offline senso

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Re: SPI rom Clear CMOS how does it actually work?
« Reply #1 on: April 14, 2020, 12:00:18 am »
Usually what it does is that the battery powers some RAM, so that its non volatile when power is removed, either that NVRAM is on the EC, or its inside the PCH(chipset) itself, never paid much attention about that part.

What kind of mods are you doing in a laptop BIOS that brick it so hard that you need to re-flash it?
 
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Offline ESXiTopic starter

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Re: SPI rom Clear CMOS how does it actually work?
« Reply #2 on: April 14, 2020, 12:36:17 pm »
Usually what it does is that the battery powers some RAM, so that its non volatile when power is removed, either that NVRAM is on the EC, or its inside the PCH(chipset) itself, never paid much attention about that part.
Alright, sounds interesting.

What kind of mods are you doing in a laptop BIOS that brick it so hard that you need to re-flash it?
Just messing around already have made it so I can program the soic 8 and a few dip switches. Just playing around. Have a not fully supported cpu in it now, it works but when loading a OS system crashes. Ordered a compatible chip. Was just testing a few things now like disabling cpu features but now sleep led indicator stays on and hdd activity led flashes. I can reprogram the spi and it works again because it resets to defaults. So Idk, is it really on the pch or ec. I see the traces from the spi rom go to the pch (true).

Looked at a SuperMicro PDSBM-LN2+ board and I traced back "Clear CMOS" jumper JBT1 to Intel NH82801GR I/O controller. Hmm, I traced the wrong trace or can this be right. Could not find a pinout so can't say for sure to what pin it goes.
« Last Edit: April 14, 2020, 12:39:00 pm by ESXi »
my elcheapo lab:
Hantek DSO5102P, KSGER T12 STM32 V2.1S + safety mods, RD6018W DC variable power supply, Quick 861DW, Quick 201B, Telequipment D1011, Optika ST-50LED (ringlight modded)
 


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