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162 www.xilinx.com Spartan-6 FPGA Configuration User Guide
UG380 (v2.7) October 29, 2014
Chapter 10: Advanced JTAG Configurations
Internal pull-up and pull-down resistors should be considered when test vectors are being
developed for testing opens and shorts. The HSWAPEN pin determines whether the IOB
has a pull-up resistor. Figure 10-3 is a representation of Spartan-6 FPGA boundary-scan
architecture.
Bit Sequence Boundary-Scan Register
The order of each non-TAP IOB is described in this section. The input is first, then the
output, and finally the 3-state IOB control. The 3-state IOB control is closest to the TDO.
The input-only pins contribute only the input bit to the boundary-scan I/O data register.
The bit sequence of the device is obtainable from the Boundary-Scan Description Language
Files (BSDL files) for the Spartan-6 family. (These files can be obtained from the Xilinx
software download area.) The bit sequence always has the same bit order and the same
number of bits and is independent of the design.
For boundary-scan testing with a configured FPGA, the Xilinx BSDLAnno utility can be
used to automatically modify the BSDL file for post-configuration interconnect testing.
The BSDLAnno utility obtains the necessary FPGA design information from the routed
NCD file, and generates a BSDL file that reflects the post-configuration boundary-scan
architecture of the device. For more information, see the BSDLAnno chapter in
UG628,
Command Line Tools User Guide.
Instruction Register
The Instruction Register (IR) for the Spartan-6 device is connected between TDI and TDO
during an instruction scan sequence. In preparation for an instruction scan sequence, the
instruction register is parallel-loaded with a fixed instruction capture pattern. This pattern
is shifted out onto TDO (LSB first), while an instruction is shifted into the instruction
register from TDI.
X-Ref Target - Figure 10-3
Figure 10-3: Spartan-6 FPGA Boundary-Scan Logic
D Q
1
0
1x
01
00
1x
01
00
1x
01
00
D Q
D Q
1
0
1
0
DQ
LE
sd
sd
LE
DQ
sd
LE
DQ
TDI
IOB.I
INTEST
IOB.O
IOB.T
EXTEST
SHIFT CLOCK DATA
REGISTER
TDO UPDATE INTEST is OR'd with EXTEST
UG380_c10_03_102014
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