Noob question about backup RAM

Mr. Mort

Another Striker
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Jan 21, 2014
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324
Ok, dumb question:

What kind of data is stored in the backup RAM? What is it's role in the overall MVS hardware?

The reason I ask is that I occasionally have games act very strangely or glitch, and the only way I can seem to correct the issue is by clearing the backup RAM on the hardware test menu.

For example, my copy of Metal Slug X would actually show up as Metal Slug 4 in the soft-dip menu and display JPN text even tho I set the Unibios to Arcade/USA. The cart passed the CRC check, but was still acting strange until I cleared the backup ram.

I also had Metal Slug 4 behave bizarrely in the past until I clear the backup RAM.

Is this normal, and should I be clearing the backup RAM every now and then?

Sorry, I know next to nothing about hardware and such, just want to know if this is normal or not.
 

HeavyMachineGoob

My poontang misses Lenn Yang's wang
10 Year Member
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Apr 3, 2011
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Backup RAM stores soft dip settings, bookkeeping, date/time and similar BIOS-related things. If the Backup RAM becomes corrupted, it can interfere with the Work RAM which is where the 68000 CPU executes game program code. This is because both the Work and Backup RAM are on the same address/data bus, they are just decoded at different address ranges using the enable lines on the SRAM chips themselves. To clear the Backup RAM, turn all hard dips on and start up the MVS. Leaving the board on Work RAM Test for upwards of an hour will allow time for the BIOS to verify the Work RAM and Backup RAM. The text "Work RAM Test" will remain unless an error is found.
 
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Mr. Mort

Another Striker
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Jan 21, 2014
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324
Thanks for the heads-up. I was also having an issue with MS3 not playing any sound at all, and it gave me a very quick M1 error before the game started. Similarly, MSX was missing just the sound in the opening sequence when the letters are smashing into the background, but was otherwise fine.

The carts looked clean, but I cleaned them anyways along with the cartridge slot. I fired a bunch of games up a number of times, and it seems fine for now, but I'm still not convinced. If I run into issues again, I'll open up the Omega and try the work RAM test.

I appreciate the info.
 

Neo Alec

Warrior of the Innanet
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Dec 7, 2000
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If you insert a new game and it's glitched during that initialization of the soft dips and other data (usually due to dirty cart contacts), then the game will often behave weirdly until the backup ram is reset. The quickest way to reset is in the hardware test menu.
 
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