Intel 8202A DRAM controller

[Bentendo64]

I have these dynamic ram controller chips - the Intel 8202A. I also have a bunch of 2104 DRAM chips, and I would like to use them in a homebrew computer I am working on. However, I have found conflicting information regarding the 8202A's. Take a look at these datasheets:

http://pdf.datasheetarchive.com/datasheetsmain/Datasheets-110/DSAP005671.pdf
http://pdf.datasheetarchive.com/datasheetsmain/Databooks-2/Book261-1008.pdf
http://pdf.datasheetarchive.com/indexerfiles/Scans-060/DSA2IH0072578.pdf

The first one claims to know nothing about "4k" mode for use with 2104's, but the next two both state that 4k mode is enabled by connecting pin 18 (AL6) to +12v through a 5.1k ohm resistor. So which is correct? Is there a 4k mode? Does anyone have any experience with these chips?

Also, I don't know if I've posted here before, but I've had an account for a year or so. I mostly just lurk

 

[jjhdnd]

The "Advance Information" data sheet describes Option 3. The "production" data sheet omits option 3 and explicitly states that there are TWO strapable options. The application note was likely written before the data sheet was finalized. The only function of Option 3 is to reduce the refresh rate to get the most efficient use from the 4K chips. If you can give up a little efficiency (cough) using those 4K chips, you don't need to bother with that option. The option may actually be functional in the production chips, but the market demand did not justify the factory testing that it would require to certify the function. You really don't need the option, just use the chips and and connect AL6 and AH6 to ground.

 

[Bentendo64]

Yeah, I figured I'd try it and if it doesn't work, oh well. I figured I'd just use it anyway without 4k mode, just refresh would take a bit longer and therefore performance decrease (although not by much, it would just be counting through one extra row). The issue that would come up though is if I had multiple banks of 4k. The first bank would be mapped at let's say, address 0. The next bank would start at 4000hex. Though I could probably just do some magic and decide which bank gets RAS for reads and writes myself.

 

[jjhdnd]

The bank selection is determined by the B0, B1 inputs. For 4K chips, don't use AL6, AH6. Connect your system A0 - A5 to to the 8202's AL0 - AL5, your system A6 - A11 to the 8202's AH0 - AH5, your system A12, A13 to the 8202's B0, B1. You will have four contiguous banks of 4K each.

 

[Chuck(G)]

A quirky chip. I remember one of the engineers sitting with the datasheet and mumbling that if you run the timings out to their limits, you can end up in a situation that requires a negative access time for the DRAM. We used 4116/2117 chips.

 

[eeguru]

Any particular reason you are using the 8202A? SRAM was around in similar or even smaller board densities, however it was very costly in the era. The only motivation for DRAM was cost. Today designing a new old computer doesn't have that restriction.

I only ask as I imagine finding 8202As are a real pain in 2015. I just hope your project doesn't help drive a 'working-pull' demand.

 

[Bentendo64]

The bank selection is determined by the B0, B1 inputs. For 4K chips, don't use AL6, AH6. Connect your system A0 - A5 to to the 8202's AL0 - AL5, your system A6 - A11 to the 8202's AH0 - AH5, your system A12, A13 to the 8202's B0, B1. You will have four contiguous banks of 4K each.

Oh, duh. I don't know what I was thinking of when I wrote that.

Anyway, my motivation for using these chips this day and age is the fact that I have 24 2104 DRAM chips, and I'm not the kind of person who likes stuff like that sitting on the shelf doing nothing. I have no idea how likely any of them are to be functional, but it would be fun to try at least.
You can get 8202A's on ebay fairly easily and not terribly expensive. I got the ones I have on ebay from that UTSource seller. I don't know about the chips, though because they look absolutely perfect, so I don't know if that might indicate they are fakes. The only way to know is to try, I guess!