One Night, While Pondering The Sst49lf020...., SST 020 not so different than 020A ??? Options

[s_cube]

g'day scene,
there is something someone had said to me a bit ago, and it is buggin me. I think the person was trying to say (it was a german fellow and my german is not that great ), that the important difference between the SST 49LF020 and SST 49LF020A was that the latter "could not be programmed in an LPC programmer, you need a good flash programmer".
This person was basically trying to say that there was little difference between these two versions, implying I could use it in my 'ole cheapmod socket/whateverchip, but I quickly dismissed that...
I've searched a bit on why you can't use 020A in place of 020 model, but I don't know enough about how the flashroms are interfaced to know truly if this is just horseshit. I'm thinking it's a crock, but still wanted to ask the community.
Thanks all,

scube

[antz1970]

the reason the standard sst20 worked in the xbox was actually due to a bug in the chip , the sst20 is now no longer in production and has been replaced by the sst20a , the bug has now been fixed tho so it will no longer work as a cheapmod. they can still be made to work in an xbox but they need a lattice chip with cpld code to recreate the original bug of the old sst20

[s_cube]

So the cheapmods and co. took advantage of a flaw in the design of the original 020? man, I need to dig deeper on this one...
Was it a flaw, or just an oversight in the design? And the lattice chip holds the code to recreate the flaw? Is this all in lamens terms? hehe....
I figured another chip holding any code could just move data around however needed and just "work with" the 020A, meaning reroute data or translate it for the new chip. Tho, I guess thats what you meant, thanks for the info ...


scube

[ckh2004]

Xbox needs 1MB of bios. The reason why SST 49LF020 can be wired directly to the LPC port of xbox (cheapmod) is that the bug in 49LF020 duplicates the 256KB bios space / bank four times to give the required 1MB bios. 49LF020A fixed this bug, so it is no longer possible to fake 1MB bios out of 256KB flashrom. Maybe SST was under pressure to fix / close the bug or loop hole that allows 49LF020 to be used as cheapmod, which is basically just a low cost flashrom without the need for extra (expensive) CPLD. All other flashroms require a CPLD (Lattice or Xlinx) to recreate a 1MB bios out of smaller bank.

[s_cube]

excellent data,
thanks chk2004!

This clears up alot of my misunderstanding here. When I heard that the 020 versions were flawed I immediately wondered if they went to 020A due to some pressure from somewhere...

s_cube

[hippo]

The changes between the 020 and 020A are naturally developing changes. They added a way to have a 4 mb bios using 16 020A's mapped to their own memory blocks so one bios loads off 16 chips.

Maybe it's MS that utilized the feature in the 020 to get it working or maybe the technology was such that this was the first and only chip available to use. It makes sense if you were coding the MCPX chip and making a routine to load a flashrom from the LPC that you would have a specific chip in mind for the LPC and since we haven't found any other flashrom device that responds to the Xbox LPC bus like the 020 it's pretty safe to assume MS had the 020 in mind from the ground up.

I might be wrong and we might still find another device that works nativly with the MCPX on the LPC bus. Of all the chips I've looked at the data sheets on (about 10 or so) the one most closely matching the expected responses of the 020 is the chip Doux first started with. This however is a 5v parallel flashrom and probably not what MS had in mind when they coded the MCPX to load the LPC.