16
AT40K Series Configuration
1009B–FPGA–03/02
Full vs. Partial
Bitstreams
In programming an AT40K series FPGA, the user will normally load the entire configura-
tion SRAM memory map from start to finish. This requires a full bitstream. Bitstream
sizes are shown in Table 8.
It is possible, by using the windowing mechanism, to download the SRAM memory map
in smaller segments. By this means, the user may load portions of the array before oth-
ers, eliminate the loading of unused portions of the array, and overwrite previously
written portions of configuration SRAM with new design information.
AT40K software tools (Atmel’s FPGA Integrated Development System) supports bit-
stream compression. Please refer to the IDS Software User Guide for more information.
Check Function
The AT40K family supports a Check Function on configuration SRAM data (a write ver-
ify). This is accomplished by normally initiating a configuration download while driving
CHECK Low. Instead of writing the contents of the bitstream to memory, the contents of
memory are instead read and compared to the bitstream on a byte-by-byte basis in the
configuration logic. Any differences are reported by driving the INIT pin Low. The INIT
pin will lower two clocks after the miscompare. The Check Function is available after
power-on-reset and manual reset, and can be performed on an “empty” FPGA prior to
the first programming of the device. Windowed or non-windowed bitstreams may be
checked. Although the check function does not write the FPGA SRAM contents, the
configuration control register is written. The configuration control register is not checked.
Start and End addresses are examined for integrity, as they are in every download, but
only the data at those addresses are “checked”. The contents of the Checksum registers
cannot be verified with the Check Function.
The maximum CCLK frequency when performing a Check Function is much lower than
that of a normal download. Exact timing specifications are listed under the mode
descriptions later in this document.
The bitstream will not be terminated on a Check Function error.
Table 8.
AT40K Series Bitstream sizes
Device
Array Size
Bytes
Bits
AT40K05
16 x 16
5263
42104
AT40K10
24 x 24
11175
89400
AT40K20
32 x 32
19279
154232
AT40K30
40 x 40
29575
236600
AT40K40
48 x 48
42063
336504
