problem in adding SDRAM with chipset VXPRO+

[RANSLANT]

*** see more and conclusion at the end ***
i have a motherboard vxpro+ with 4 simm slots and 2 dimm slots .
previously, i used the 4 simms with 48Meg and i'm trying to add a 64Meg SDRAM in the first dimm slot. But i get only 16Meg more !!
Is there anynone who knows anything about this problem

The documentation with the motherboard shows that i can use DIMM an SIMM simultaneously, execpt that i can't use DIMM2 and SIMM 1 & 2 a the same time

*** more
i got confirmation by several vendors that
VXPRO+ doesn't support SDRAM with 64 MB but only 32MB, i'll try that soon. I mean SDRAM at 66Mhz, but 100Mhz SDRAM should work too.
The only thing you can't do, is to use SDRAM
at 66Mhz with motherboard at 100Mhz.

*** and more
i tried a 32 MB SDRAM. It works !
you can see on www.pcchips.com that their VXpro+ motherboards don't support any 64MB SDRAM

[This message has been edited by RANSLANT (edited 03-09-99).]

[This message has been edited by RANSLANT (edited 03-11-99).]

[Symes]

I've got a VX-Pro+ board too, and used to use all the SIMM slots. But I changed to a single 64MB DIMM, and removed the SIMMs (there are reports of mixed memory effecitively slowing down to the lowest common denominator) It works fine.

Have you tried with just the DIMM fitted to ensure it's OK? and then trying just two of the SIMMs fitted to Slot 1/2 and/or 3/4 to see if you can at least see 32Mb(SIMM) and 64Mb(DIMM)?

It would also be worth moving the DIMM to the other socket, the documentation might be wrong!

I'll give the SIMM/DIMM shuffle a try on my board and let you know.

BTW - If yours is a PCChips VX-Pro, you might like to checkout www.zarniwoop.force9.co.uk where I've posted the mods required to the board to get 4.5 multipliers and <2.5Vcore.

[This message has been edited by Symes (edited 03-05-99).]

[sfarley]

It is never advisible to mix simms and dimms. Think about it. The cpu is sending and receiving info. from chips that are running at two different speeds. Sounds confusing? It is to the cpu. Trade someone for some more sdram. Now, you can mix pc100 and 10ns sdram. The only thing is, all the sdram will run at the lower speed.

[Peter M]

Hi!

The "VXpro+" chipset (VIA VPX/97 actually) does not support 64 MBit SDRAM chips, so you can't add a large DIMM successfully.

And, more importantly, in general you cannot mix DIMM and SIMM unless the board has separate power supplies and line drivers - you either fry your DIMMs at 5V, or undersupply your SIMMs at 3.3V. Most boards do not provide the extra circuitry, only some Gigabyte models did.

Regards, Peter

[Symes]

Peter,

I've got a single 64Mb DIMM in my M537dma (VX-Pro+) and it works fine. It is only PC66 though, maybe that's the reason?

[smunzli]

if both the simm and dimm are running the same bus rate than it will work. but if your dimm is pc100 forget it. no board runs 66 and 100 mhz front ends at the same time. you would need two set of timers on board. i would look at the dimm and see if it pc100, also the chip set you speak of has auto mem config so it see the fastest mem.

[Peter M]

Smunzli,

you're talking nonsense. A DIMM being "PC100" only means it is _capable_ of running at 100 MHz reliably. If you stick a PC100 DIMM into a 66 MHz machine, it will be run at 66 (and also work reliably). The DIMM does not create its bus clock. The chipset runs the RAM datapath at a given speed, and the DIMMs and SIMMs must be able to cope.

All SIMM/DIMM capable chipsets are able to access one bank in EDO/FPM mode and another in SDRAM mode.

The problem in mixing them is that EDO/FPM banks need 5V power supply and I/O signalling, while SDRAMs are 3.3V parts and almost no SDRAM chip is 5V tolerant on its I/O lines. So you're either going to fry your SDRAM's I/O lines or undersupply your EDO/FPM memory.


Symes,

Not having 64 MBit _chip_ support does not necessarily mean you can't use a 64 MByte _DIMM_. You can, as long as this particular DIMM has chips with 16 MBit technology on it.

Maybe you share the information with us - is there any manufacturer/part no. on the DIMM, and what's written on the chips themselves?


Regards, Peter

[Symes]

Peter,

Apologies I hadn't considered the Mbit/byte difference!

My 64MByte DIMM is made up of 8 chips, each are marked;

9818 A USA
MT 48LC8M8A2
TG -10

Ranslant,

Checkout BXBoards.com (or something like that) where there are lists of 'PC66' chips that work very well at 100Mhz!

[Peter M]

Thank you Symes!

I checked with Micron Technology what those SDRAMs are, and surprise surprise ... they are 64 MBit! They are a more unusual 8MBit x 8 Bit type (rather than the more common 16x4), which obviously is working with the VIA VPX/97 "VXpro+" (although both VIA and PC-Chips deny 64 MBit support here).

Good news. Still got one guy who needs more RAM on his M537+, now let's see if I find such a DIMM here.

Regards, Peter

[Symes]

Thanks for the info Peter!

I must have just been lucky when I ordered the memory from a local guy because I didn't specify the board they were going into! Sometimes it happens that way!

If it's any help my board is (from memory)version 5.2.