R
XC5200 Series Field Programmable Gate Arrays
Table 11: XC5200 Bitstream Format
CCLK and address signals continue to operate externally.
The user must detect INIT and initialize a new configuration
by pulsing the PROGRAM pin Low or cycling Vcc.
Data Type
Value
Occurrences
Start Byte
11111110
Once per data
frame
Data Frame *
DATA(N-1:0)
Table 12: Internal Configuration Data Structure
Cyclic Redundancy Check or
Constant Field Check
CRC(3:0) or
0110
PROM
Size
(bits)
Xilinx
Serial PROM
Needed
Fill Nibble
1111
VersaBlock
Array
Device
Extend Write Cycle
Postamble
FFFFFF
11111110
FFFF…FF
FF
Once per de-
vice
Fill Bytes (30)
Start-Up Byte
XC5202
XC5204
XC5206
XC5210
XC5215
8 x 8
42,416
XC1765D
Once per bit-
stream
10 x 12
14 x 14
18 x 18
22 x 22
70,704
XC17128D
XC17128D
XC17256D
XC17256D
106,288
165,488
237,744
*Bits per Frame (N) depends on device size, as described for
table 11.
Data Stream Format
Bits per Frame = (34 x number of Rows) + 28 for the top + 28 for
the bottom + 4 splitter bits + 8 start bits + 4 error check bits + 4 fill
bits * + 24 extended write bits
The data stream (“bitstream”) format is identical for all con-
figuration modes, with the exception of Express mode. In
Express mode, the device becomes active when DONE
goes High, therefore no length count is required. Addition-
ally, CRC error checking is not supported in Express mode.
= (34 x number of Rows) + 100
* In the XC5202 (8 x 8), there are 8 fill bits per frame, not 4
Number of Frames = (12 x number of Columns) + 7 for the left
edge + 8 for the right edge + 1 splitter bit
= (12 x number of Columns) + 16
The data stream formats are shown in Table 11. Express
mode data is shown with D0 at the left and D7 at the right.
For all other modes, bit-serial data is read from left to right,
and byte-parallel data is effectively assembled from this
serial bitstream, with the first bit in each byte assigned to
D0.
Program Data = (Bits per Frame x Number of Frames) + 48
header bits + 8 postamble bits + 240 fill bits + 8 start-up bits
= (Bits per Frame x Number of Frames) + 304
PROM Size = Program Data
7
Cyclic Redundancy Check (CRC) for
Configuration and Readback
The configuration data stream begins with a string of eight
ones, a preamble code, followed by a 24-bit length count
and a separator field of ones (or 24 fill bits, in Express
mode). This header is followed by the actual configuration
data in frames. The length and number of frames depends
on the device type (see Table 12). Each frame begins with
a start field and ends with an error check. In all modes
except Express mode, a postamble code is required to sig-
nal the end of data for a single device. In all cases, addi-
tional start-up bytes of data are required to provide four
clocks for the startup sequence at the end of configuration.
Long daisy chains require additional startup bytes to shift
the last data through the chain. All startup bytes are
don’t-cares; these bytes are not included in bitstreams cre-
ated by the Xilinx software.
The Cyclic Redundancy Check is a method of error detec-
tion in data transmission applications. Generally, the trans-
mitting system performs a calculation on the serial
bitstream. The result of this calculation is tagged onto the
data stream as additional check bits. The receiving system
performs an identical calculation on the bitstream and com-
pares the result with the received checksum.
Each data frame of the configuration bitstream has four
error bits at the end, as shown in Table 11. If a frame data
error is detected during the loading of the FPGA, the con-
figuration process with a potentially corrupted bitstream is
terminated. The FPGA pulls the INIT pin Low and goes into
a Wait state.
During Readback, 11 bits of the 16-bit checksum are added
to the end of the Readback data stream. The checksum is
computed using the CRC-16 CCITT polynomial, as shown
in Figure 23. The checksum consists of the 11 most signifi-
cant bits of the 16-bit code. A change in the checksum indi-
cates a change in the Readback bitstream. A comparison
to a previous checksum is meaningful only if the readback
data is independent of the current device state. CLB out-
puts should not be included (Read Capture option not
used). Statistically, one error out of 2048 might go undetec-
ted.
In Express mode, only non-CRC error checking is sup-
ported. In all other modes, a selection of CRC or non-CRC
error checking is allowed by the bitstream generation soft-
ware. The non-CRC error checking tests for a designated
end-of-frame field for each frame. For CRC error checking,
the software calculates a running CRC and inserts a unique
four-bit partial check at the end of each frame. The 11-bit
CRC check of the last frame of an FPGA includes the last
seven data bits.
Detection of an error results in the suspension of data load-
ing and the pulling down of the INIT pin. In Master modes,
November 5, 1998 (Version 5.2)
7-107
ETC [ ETC ]
