Altera discovered that metastability on the address registers in any of the memory blocks can corrupt the memory contents. The following note was added to
Figures 7-9 through 7-13 in the Cyclone Handbook and will be added to Figures 8-13 through 8-20 in Cyclone II handbook:
Note: Violating the setup or hold time on the address registers could corrupt the memory contents. This applies to both read and write operations.
Also, on page 7-4 in Cyclone Handbook the following text was added and on page 2-28 of Cyclone II handbook, just above the footnote, the following text will be
added:
"Violating the setup or hold time on the memory block address registers could corrupt memory contents. This applies to both read and write operations."
This will be fixed in a future version of the Cyclone II device handbooks. This was already fixed in Cyclone Handbook version 1.5.