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78 www.xilinx.com Spartan-6 FPGA Configuration User Guide
UG380 (v2.7) October 29, 2014
Chapter 5: Configuration Details
Bit Swapping
Bit swapping is the swapping of the bits within a byte. The MCS, EXO, and TEK PROM file
formats are always bit swapped. The HEX file format can be bit swapped or not bit
swapped, depending on user options. The bitstream files (BIT, RBT, and BIN) are never bit
swapped.
The HEX file format contains only configuration data. The other PROM file formats
include address and checksum information that should not be sent to the FPGA. The
address and checksum information is used by some third-party device programmers, but
it is not programmed into the PROM.
Figure 5-1 shows how two bytes of data (0xABCD) are bit swapped.
The MSB of each byte goes to the D0 pin regardless of the orientation of the data:
In the bit-swapped version of the data, the bit that goes to D0 is the right-most bit.
In the non-bit-swapped data, the bit that goes to D0 is the left-most bit.
Whether or not data must be bit swapped is entirely application-dependent. Bit swapping
is applicable for Master Serial, Master SelectMAP, or BPI PROM files.
X-Ref Target - Figure 5-1
Figure 5-1: Bit Swapping Example
UG380_c5_01_042909
Hex:
Binary:
Bit-
Swapped
Binary:
Bit-
Swapped
Hex:
SelectMAP
Data Pin:
D0 D1 D2 D3 D4 D5 D6 D7 D0 D1 D2 D3 D4 D5 D6 D7
1 0 1 0 1 0 1 1 1 1 0 0 1 1 0 1
A B C D
1 1 0 1 0 1 0 1 1 0 1 1 0 0 1 1
D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0
D 5 B 3
SelectMAP
Data Pin:
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