Help with a 48k ram card

[chriswhit]

I'm building a 48k ram cart for use with a 7800 dev. system. I'm using a Hat trick cart. My question is weather this ram chip and capacitor will work? If not what do I need and where can I get them? Thank youhttp://cgi.ebay.com/0-1-uF-50V-Axial-lead-X7R-Ceramic-Capacitors-100-pcs_W0QQitemZ180434359919QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item2a02b9d66f

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=330295275302&ssPageName=STRK:MEWAX:IT

http://cgi.ebay.com/0-1-uF-50V-Axial-lead-X7R-Ceramic-Capacitors-100-pcs_W0QQitemZ180434359919QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item2a02b9d66f

Edited November 19, 2009 by chriswhit

[+Mitch]

The capacitor should be fine, though I usually just reuse the one that's already on the board. It should be fine unless you cooked it when you removed it. I am not familiar with that particular RAM chip but I think it should work.

 

Mitch

[gdement]

Those RAM chips are in SOJ packaging. I've never built a RAM cart but I assume you would want DIP style, not surface mount.

Edited November 20, 2009 by gdement

[chriswhit]

Those RAM chips are in SOJ packaging. I've never built a RAM cart but I assume you would want DIP style, not surface mount.

Where do I find DIP style ram? I want to do this right as this will be used a lot. Thanks

[gdement]

I'd order them from Jameco, but there's also probably other places.

 

 

This will give you their SRAM section:

http://www.jameco.com/webapp/wcs/stores/servlet/StoreCatalogDrillDownView?langId=-1&storeId=10001&catalogId=10001&categoryName=cat_1050&subCategoryName=ICs%20%26%20Semiconductors%20%2F%20Memory%20%2F%20SRAM&category=105090

 

Click on "configuration" and select either 32Kx8 (for an 8-bit 32KB chip) or 128Kx8 (for a 128KB chip). I'm not sure what you use when building a 48K cart.

Note that there aren't any 64KB chips. For whatever reason SRAM is only made in multiples of 4.

Make sure anything you look at is DIP (DIP-28 means DIP package with 28 pins).

 

For the 32KB chips, part number 62256 should work. Jameco is selling 62256LP but I think that just means it's "low power", which shouldn't hurt anything. I don't know how much speed is required but 120ns should be plenty fast enough:

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=42850

 

Note that the package is marked as "DIP-28" - for any chips you look at make sure it's a DIP package. Those are by far the easiest to solder by hand, are what Atari used, and are probably what you had in mind. I'd also download the datasheet for whatever you order to confirm the pinout matches what you need, and that it runs on 5V.

 

There's probably 62256 chips available lots of places, Jameco is just a place I'm used to ordering from.

I've never built a RAM cart, so I could be mistaken about the 62256, but I think it's what Atari used.

 

 

For 128KB chips, it looks like they only have 2 in DIP-32 that run on 5V:

http://www.jameco.com/webapp/wcs/stores/servlet/StoreCatalogDrillDownView?langId=-1&storeId=10001&catalogId=10001&position=1&refineType=1&sub_attr_name=Configuration&refineValue=128k%20x%208&refine=1&history=h01k7me3%7CsubCategoryName~ICs%2B%2526%2BSemiconductors%5Ecategory~10%5EcategoryName~category_root%5EprodPage~15%5Epage~SEARCH%252BNAV%407w9oh64b%7Ccategory~1050%5EcategoryName~cat_10%5Eposition~1%5Erefine~1%5EsubCategoryName~ICs%2B%2526%2BSemiconductors%2B%252F%2BMemory%5EprodPage~15%5Epage~SEARCH%252BNAV%40jxv1snk4%7Ccategory~105090%5EcategoryName~cat_1050%5Eposition~1%5Erefine~1%5EsubCategoryName~ICs%2B%2526%2BSemiconductors%2B%252F%2BMemory%2B%252F%2BSRAM%5EprodPage~15%5Epage~SEARCH%252BNAV

 

Those are part 628128LP. I don't know if those work or not, but I assume they would. Definitely check the pinout first.

Edited November 25, 2009 by gdement