I want to be able to choose between 64Mb:x16 SDRAM, 128Mb:x16 SDRAM and 256Mb:x16 SDRAM memory in my hardware design. I read in the NS7520 Hardware Reference (Section: Using the internal multiplexer) that the RAS stage is pointing out the logical address A22-A9 and the CAS stage is pointing out the logical address A10-A1. This seem to be okey for 64Mbit SDRAM but not for larger memory sizes because the logical address A9 is pointed out in both RAS and CAS. I have checked with Micron and Samsung SDRAM without success. My questions are: - Is possible to use 128Mb:x16 SDRAM and 256Mb:x16 SDRAM with the NS7520? - In that case how and for which memories is this possible (manufacturer and type)?
The NET+50 and the NS7520 do not support any SDRAM’s with more than 8 CAS inputs. The 128MB and 256MB both have more than 8 CAS inputs. This is a limitation of the SDRAM controller.
… there are reference designs on the Netsilicon Web site showing how to hook up larger SDRAMs using an external multiplexer… BBFN Dave