06-12-2014 05:22 AM
I have a question about the available models on the ibis file of the Virtex7. Indeed, I have not found a response on the document, thus I need help.
I would like to know what is the difference between models "SSTL18_I_S" and SST18_II_S" for example ? It seems to be 2 types of models, type I and type II but I don't find any details about that...
Please if you have any issue...
06-12-2014 05:38 AM
06-13-2014 03:42 AM - edited 06-13-2014 03:44 AM
The termination style (class-I & class-II) required is based on the DDR memory application.
SSTL18 is defined by the JEDEC standard JESD8-15, and is used for DDR2 SDRAM memory interfaces.
The class-I driver can only be used in unidirectional topologies (no bidirectional support).
The class-II driver can be used for both for bidirectional and unidirectional signaling. For some topologies (such as short, point-to-point interfaces), the class-I driver can result in reduced overshoot and better signal integrity.