FPGA memory module specifications

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edenist
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FPGA memory module specifications

Post by edenist » Mon Jun 23, 2014 1:24 pm

Thanks so much for posting up the umdk as open source!

I've been re-acquainting myself with assembly with some mega drive programming, and have been wanting to move over to working on real hardware for some time, so this project has finally given me the motivation to do so!

I've been sourcing components to assemble my own lx9 and umdk boards, and I have a couple of questions regarding some components.

For the FPGA RAM chip, the PCB files and gerbers have listed IS42S16400-TSOP54, which is an ISSI part. The HaD.io page lists part MT48LC8M16A2P-7E.
These parts are identical in most specifications except for frequency and capacity.

The ISSI chip is listed as 8MiB at 143MHz
The Micron chip is listed as 16MiB at 133MHz

Is the 16MiB capacity the correct one? Also, how sensitive is the FPGA to 143MHz vs 133MHz memory?

Thanks very much once again for sharing your work!

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prophet36
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Post by prophet36 » Mon Jun 23, 2014 1:56 pm

Hi edenist,

You're right, that is confusing. The LX9 PCB has always had the ISSI part number. Because the addresses will just wrap at 8MiB, there's nothing stopping UMDK working with an 8MiB (64Mib) SDRAM like the ISSI chip, but technically you should use a 16MiB (128Mib) SDRAM, otherwise some of the code will be a bit confusing.

The LX9 board should also work with a 256Mib SDRAM like the Samsung K4S281632F, but I have not tried it yet - unfortunately only half of the RAM will be available (unless you solder a flying lead and give up one of the I/Os), but it's a bit easier to find (and probably cheaper) than the 128Mib parts. I have bought a batch of K4S281632F from aliexpress.com so I should know in a few weeks whether it'll work.

As far as speed is concerned, the FPGA is currently system-synchronous at 48MHz. Having just one clock-domain simplifies the logic enormously. The SDRAM is only clocked at 48MHz, but it does a read (and a write, and a refresh) in four cycles (Reads: ACT, READ, NOP, PRE; Writes: ACT, WRITE, NOP, PRE; Refresh: REF, NOP, NOP, NOP). So the important thing is to check the timings to ensure that scheme will work. In practice, any 128Kib 133MHz-or-faster TSOP-54 SDRAM should work fine. 100MHz may be pushing it a bit.

How are you fixed for PCBs? I may be able to sell you an LX9+Bridge pair at cost ($11.24 plus postage from the UK). I need to check how many I've got left.

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edenist
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Post by edenist » Mon Jun 23, 2014 2:35 pm

Hi prophet36,

Thank you very much for the (extremely) fast reply!

That really clears up my queries regarding the SDRAM chips. I've got a supplier locally with plenty of the Micron 128Mib available, so I will grab a few of those.

I haven't arranged my PCB fabrication yet. I have taken a look at hackvana whom you linked to, but I haven't had a chance to request a quote.

If you have some boards available still, I would love to purchase a pair off you. I am more than happy to pay for shipping from the UK as well.
If you have any available it would certainly be appreciated :-)

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Post by prophet36 » Mon Jun 23, 2014 2:44 pm

edenist wrote:If you have any available it would certainly be appreciated :-)
It looks like you're in luck - I have one bridge PCB left (and several LX9 PCBs). If you PM me your address (and email) I'll send you a PCB pair.

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