DDR Address

Hi, Is it ok not to connect at least one DDR Address signal to a ddr controller? If so, should i connect it to GND or VCCIO? Thanks.

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yy
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Might be some trouble if this is an SDRAM with a control register. What are you up to?

Reply to
Brad Smallridge

Ayon kay Brad Smallridge:

Hi Brad, My design is out of IO pins, BTW i use an FPGA ddr controller core..

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yy

The main thing you need to be careful of is the initialization phase of the DDR (assuming you need initialization). This requires that you be able to access certain specific addresses.

Reply to
Duane Clark

This is such an odd question. The obvious answer is look at the datasheet on the ddr. ddr needs to be configured. This is done by putting a special address on the address lines. Which address bits need to be changing? Which can be tied to 0 or 1, or another address bit? Every address bit you remove will knock out at least 50% of the storage capacity of the ram, and these accumulate. Lose enough bits and the bits start knocking out 75% of the remainder. You've also got 2 bank bits -- you can tie them together. Or tie them to 0, at the expense of losing 50% or 75% of capacity.

So you're out of io pins, but the design isn't finalized. Get a more io-centric part. This is like a jockey who's worried about being too heavy, so he's wondering if he cuts off a hand will he be able to handle the horse?

There just isn't enough information in your question to go on. Failing that, you've got to do the studying and figure it out for yourself. I would think it's certainly possible to cut out pins to the DDR, but at what cost? You've got to figure that out.

A better approach to reducing pins, ddr related, might be to let data pins float, or perhaps get an 8 bit part instead of a 16 bit one. By adding one address bit you can half the number of data pins without losing memory. Probably you can tie unused data pins to a pullup or pulldown.

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David Ashley                http://www.xdr.com/dash
Embedded linux, device drivers, system architecture
Reply to
David Ashley

I guess you're right...

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