Xilinx SelectIO 7 Series User Manual page 159

a shift right by one and shift left by three. In this example, on the eighth Bitslip operation,
the output pattern reverts to the initial pattern. This assumes that serial data is an eight bit
repeating pattern.
Although the repeating pattern seems to show that bitslip is a barrel shifting operation,
this is not the case. A bitslip operation adds one bit to the input data stream and loses the
nth bit in the input data stream. This causes the operation on repetitive patterns to appear
like a barrel shifter operation.
X-Ref Target - Figure 3-11
Guidelines for Using the Bitslip Submodule
In NETWORKING mode the Bitslip submodule is available. In all other modes, the
module is not available.
To invoke a Bitslip operation, the BITSLIP port must be asserted High for one CLKDIV
cycle. Bitslip cannot be asserted for two consecutive CLKDIV cycles; Bitslip must be
deasserted for at least one CLKDIV cycle between two Bitslip assertions. In both SDR and
DDR mode, the total latency from when the ISERDESE2 captures the asserted Bitslip input
to when the "bit-slipped" ISERDESE2 outputs Q1–Q8 are sampled into the FPGA logic by
CLKDIV is two CLKDIV cycles. From an applications perspective, a single Bitslip
command must be issued for one CLKDIV cycle only. The user logic should wait for at
least two CLKDIV cycles in SDR mode or three CLKDIV cycles in DDR mode, before
analyzing the received data pattern and potentially issuing another Bitslip command. If
the ISERDESE2 is reset, the Bitslip logic is also reset and returns back to its initial state.
7 Series FPGAs SelectIO Resources User Guide
UG471 (v1.10) May 8, 2018
Input Serial-to-Parallel Logic Resources (ISERDESE2)
Bitslip Operation in SDR Mode
Bitslip Output
Operations Pattern (8:1)
Executed
Initial 10010011
1
00100111
2
01001110
3
10011100
4 00111001
5
01110010
6
11100100
7
11001001
Figure 3-11: Bitslip Operation Examples
www.xilinx.com
Bitslip Operation in DDR Mode
Bitslip Output
Operations Pattern (8:1)
Executed
Initial 00100111
1
10010011
2
10011100
3
01001110
4 01110010
5
00111001
6
11001001
7
11100100
ug471_c3_11_012211
Send Feedback
159