EP2C20F256C8N Datasheet, PDF (358/470 Pages) Altera Corporation – Cyclone II Device Handbook, Volume 1

Configuration Data Compression
Although they both use the same compression algorithm, the
decompression feature supported by Cyclone II devices is different from
the decompression feature in enhanced configuration devices (EPC16,
EPC8, and EPC4 devices). The data decompression feature in the
enhanced configuration devices allows them to store compressed data
and decompress the bitstream before transmitting it to the target devices.
In PS mode, you should use the Cyclone II decompression feature since
sending compressed configuration data reduces configuration time. You
should not use both the Cyclone II device and the enhanced configuration
device decompression features simultaneously. The compression
algorithm is not intended to be recursive and could expand the
configuration file instead of compressing it further.
You should use the Cyclone II decompression feature during AS
configuration if you need to save configuration memory space in the
serial configuration device.
When you enable compression, the Quartus II software generates
configuration files with compressed configuration data. This compressed
file reduces the storage requirements in the configuration device or flash,
and decreases the time needed to transmit the bitstream to the Cyclone II
device. The time required by a Cyclone II device to decompress a
configuration file is less than the time needed to transmit the
configuration data to the FPGA.
There are two methods to enable compression for Cyclone II bitstreams:
before design compilation (in the Compiler Settings menu) and after
design compilation (in the Convert Programming Files window).
To enable compression in the project's compiler settings, select Device
under the Assignments menu to bring up the settings window. After
selecting your Cyclone II device open the Device & Pin Options
window, and in the General settings tab enable the check box for
Generate compressed bitstreams (see Figure 13–1).
13–4
Cyclone II Device Handbook, Volume 1
Altera Corporation
February 2007