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Posted: Mon Jun 11, 2012 4:49 pm
by DNSDies
so, pulldown resistors on we and ce of the sram to ground ensures those lines stay tied to ground when powering on or off the console.
I suppose this makes it so you don't have to hold Reset when powering off?
It needs to be a 10kohm resistor?
I have a spare 1kohm, but I'd have to o buy a 10kohm.
Posted: Mon Jun 11, 2012 5:42 pm
by infiniteneslives
You want to pull down active high signals (CE)
And pull up active low signals (/CE)
You shouldn't have to deal with /WE
Don't remember what the original boards do but I think they always ground /CE and then control CE by the mapper. So you'd do similarly and only pull down the CE line.
I think they used 10K but 1K will probably work as well.
And technically since you're coping Nintendo's design it doesn't buy you out of holding reset. Although you don't have to hold if if you feel lucky...
Posted: Tue Jun 12, 2012 3:28 pm
by DNSDies
Alright, sounds cool.
I'll draw up a pretty schematic for free reference.
This battery thing seems to be a fairly common question and even with 2 days of searching I still couldn't find all the information I needed, so it might help to have a standard reference document in one place.
Do you guys have a wiki or something I could upload it to?
Posted: Tue Jun 12, 2012 4:41 pm
by tepples
DNSDies wrote:Do you guys have a wiki or something I could upload it to?
We have a wiki, but due to past abuse, I'll need to create an account for you. Just PM me the username you want to use and an e-mail address for you to get your password.
Posted: Wed Jun 13, 2012 10:35 am
by l_oliveira
Adding to what HardWareman posted, look at the BA6162 chip in special, it has two chip enables, one inverted and one non inverted.
While non inverted signal is obviously meant to be used with chips that have a additional non inverted chip select pin such as 6264 or 628128, you can use chips that only have a single inverted chip enable signal such as 62256 or 628512 with it if you do this:
Code: Select all
R/W---\
|LS32>----- SRAM /WR
/CE---/
/CE----\
|LS32>----- SRAM /OE
GND---/
Where R/W is the write strobe from the mapper or NES, where appropriated. /CE is the original chip enable strobe that would go to the SRAM chip and places it on the bus when active. This circuit frees the original SRAM /CE which will be then used to control the SRAM data integrity and switch it into low power mode when power is off.
Don't forget to have the SRAM /CE go straight to the inverted /CE output on the BA6162 chip.