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Chapter 16: PROMGen
R
–z (Enable Compression)
–z version
The –z option enables compression for a Xilinx multi-bank PROM. All version will be
compressed if one is not specified.
Bit Swapping in PROM Files
PROMGen produces a PROM file in which the bits within a byte are swapped compared to
the bits in the input BIT file. Bit swapping (also called “bit mirroring”) reverses the bits
within each byte, as shown in the following figure:
In a bitstream contained in a BIT file, the Least Significant Bit (LSB) is always on the left
side of a byte. But when a PROM programmer or a microprocessor reads a data byte, it
identifies the LSB on the right side of the byte. In order for the PROM programmer or
microprocessor to read the bitstream correctly, the bits in each byte must first be swapped
so they are read in the correct order.
In this release of the Xilinx Development System, the bits are swapped for all of the PROM
formats: MCS, EXO, BIN, and TEK. For a HEX file output, bit swapping is on by default,
but it can be turned off by entering a –b PROMGen option that is available only for HEX
file format.
Figure 16-2: Bit Swapping
X8074
Original Data
1000 1010
8A
51
Data in PROM File or HEX File
0101 0001