Honored ContributorI am trying use the DDR2 ALTMEMPHY with about 20 DDR2 chips. The local FAE says that it is only possible to use 8 chips as that is all the GUI will allow you to select. Is there a way to use a larger number of chips or is there some other method/core for this?
Thanks Trampas
Honored ContributorA standard DDR2 RAM design has usually more "chips" (e.g. a two bank 64 bit 1 GBit SODIMM module has 16), and it can be used with Altera DDR2 controller, utilizing ALTMEMPHY as physical driver. So if there is a limitation, it depends on the memory organisation.
Honored ContributorWell I would normally connect several parts up and make the memory bus wider, but I am using a small part that can only support 8 bit data bus. I guess I might have to try a few things and see what happens, I just hate to design a board not knowing.
TrampasHonored ContributorSo you want to have a 8 bit memory with 20 chips selects? Altera designers probably didn't expect this to be ever needed. Furthermore, you probably would have serious signal quality issues when connecting that many bidirectional dq and dqs pins to a single bus line.
Honored ContributorYeap, I know that it is not expected or planned.
My application does not need high speed, 60Mhz is fine but we need a lot of memory. I might be able to go back and switch to a 16bit bus. But we are really tight on pin counts. TrampasHonored ContributorYes, I see. 60 MHz is unusually slow, it should basically work without ALTMEMPHY timing calibration.
Honored ContributorYeap, thus I was not too worried about number of chips. Also design is small and with 16 chips the maximum distance from FPGA is only about 2.5"
TrampasHonored ContributorWhat sort of DDR2 chips are you planning to use? Are you aware that regular DDR2 chips usually have a minimum clock speed requirement (which is about 125MHz)?
Honored ContributorGood point. I didn't notice, cause I never planned CLK frequencies below 200 MHz.
Honored ContributorI am going to use the MT47H128M8. I did not realize the DDR2 had a minimal clock rate. I guess I need to read the datasheet a bit more.
Honored ContributorYeah, also DDR1 has a minimum clock rate of ~80MHz. Mobile DDR is the only consumer DDR with no minimum clock rate requirement, but they are more expensive.
