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PROCESSOR-SDK-C665X: Maximum DDR3 memory / Lowest Component Count

Thorsten Wronski
Prodigy 200 points
Part Number: PROCESSOR-SDK-C665X

Hello!

I think the Keystone supports maximum 8 Gigabyte RAM, is that right?

The 8 Gigabit DDR3 chip from Micron MT41K512M16HA-125 IT:A has 8Gbit = 1 Gigabyte RAM and is 16 Bits wide.   4 pieces of this device result in only 4 Gigabyte total

An alternative part with similar specification is the Intelligent Memory 8 Gigabit 1CS part# IM8G16D3FCBG-125I

a) Would it also be possible to use 8 pieces of 8 Gigabit with a 8 bit wide interface like IM8G08D3FCBG-125I or MT41K1G8SN-125 IT:A ?

b) Does the Keystone support a second  chip-select (CS), clock enable (CKE), ODT and ZQ to add a second rank of another 4 pieces of 16 Bit wide components with 8 Gigabit each?

c) If the answer to b) is yes, can I assume that it will also be possible to use 4 pieces of a future 16 Gigabit DDR3 component with two sets of CS, CKE, ODT and ZQ pins?  Intelligent Memory is planning to release such a device with dual-CS later this year. This would allow to reach total 8 Gigabyte of memory by only 4 pieces of DDR3 components!

Regards,

Thorsten

  • 0
    TI__Guru 65405 points
    The team is notified. They will post their feedback directly here.

    BR
    Tsvetolin Shulev
  • 0
    TI__Mastermind 42545 points

    Hi Thorsten,

    Based on the title of your post I am assuming you are designing with a C665x. The DDR controller in the C665x is capable of addressing 8Mbytes  but the device has only a 32bit wide external DDR3 interface. This limits your options based on today's technology. Micron does support an 8bit wide 1Gbit component  (MT41K1G8RKB-107) but four of these devices would only provide 4Gbytes.  While the  C665x devices do include the second chip select, we do not recommend attempting dual rank designs. The routing restrictions needed for dual rank are very difficult to achieve and customers have had significant difficulty get dual rank to operate robustly.

    8GBytes can be achieved with the C667x components using eight devices on the 64bit wide bus. 

    Regards, Bill

  • 0 in reply to Bill Taboada
    Prodigy 200 points

    Hi!

    I do not think the MT41K1G8RKB-107 will work as this is a twin-die product with two chip-selects = two ranks inside the DRAM already, and as you mentioned, dual rank is not recommended. Furthermore, that Micron part does not exist in industrial temperature (-40 to 95°C) and also the device is going EOL according to the roadmap.

    A 1GB = 8Gbit device with single chip-select and 8 Bit width would be either the IM8G08D3FCBG-125I from Intelligent Memory or the MT41K1G8SN-125 IT:A from Micron.

    Ok, as the C665x only allows 4GB max, let's move on to the C667x which allows 8GB on the 64 bit wide bus. Then we need to use 8 pieces of 8 Gigabit DDR3 devices with 8 bit width each (= IM8G08D3FCBG-125I or MT41K1G8SN-125 IT:A)

    While I understood that you do not recommend dual rank designs, I find it interesting that - in theory - total 8GB capacity would also be possible with only 4 pieces of 16 Gigabit DDR3 devices that are 16 Bit wide, but these components will be dual rank (two chip selects on the DRAM pinout). Yes, I did hear you saying that you do not recommend dual-rank-designs. However, if the DRAMs themselves are dual-rank (separate Chip-select, CKE, ODT, ZQ pins) and share the same address- and databus, then the routing looks very simple to me. It would be by far more complex to route separate DRAM-components for each ranks.

    Well, these 16Gb DDR3 2CS parts from Intelligent Memory are not yet on the market anyway.

    Is the 8GB capacity a physical limitation or could each rank theoretically have 8GB (by using 8 pieces of 16Gb DDR3 2CS devices in x8 bit width), so the total maybe could reach 16GB of memory capacity?

    Regards,

    Thorsten

  • 0 in reply to Thorsten Wronski
    TI__Mastermind 42545 points
    Hi Thorsten,
    The 8GB is a limitation of the internal memory controller of the SoC. Only 8GB of DDR can be addressed inside the part.
    Regards, Bill