AR# 178


XC4000: What values do rams contain immediately after configuration?


It is impossible to know what values are contained within

a RAM block used in an XC4000 design until data has been

written to the RAM after configuration has ended. It is also

impossible to set an initialization value for a RAM within

the configuration bitstream. The reason for this is that

the write enable line of the RAM may experience transitions

as the programmable interconnect points that determine its

routing are turned on by the configuration process. Because

of this, spurious values on the data input of the RAM may

be written to it.


For the XC4000 devices the only way to set the initial value of

the ram is to do a write to the ram after configuration, and

set the values at that time. The XC4000E devices allow you

to initialize the RAM to a specific state during configuration.
AR# 178
日期 03/31/2011
状态 Archive
Type 综合文章
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