R
XC5200 Series Field Programmable Gate Arrays
XC5200-Series devices can also be configured through the
boundary scan logic. See XAPP 017 for more information.
Bit Sequence
The bit sequence within each IOB is: 3-State, Out, In. The
data-register cells for the TAP pins TMS, TCK, and TDI
have an OR-gate that permanently disables the output
buffer if boundary-scan operation is selected. Conse-
quently, it is impossible for the outputs in IOBs used by TAP
inputs to conflict with TAP operation. TAP data is taken
directly from the pin, and cannot be overwritten by injected
boundary-scan data.
Data Registers
The primary data register is the boundary scan register.
For each IOB pin in the FPGA, bonded or not, it includes
three bits for In, Out and 3-State Control. Non-IOB pins
have appropriate partial bit population for In or Out only.
PROGRAM, CCLK and DONE are not included in the
boundary scan register. Each EXTEST CAPTURE-DR
state captures all In, Out, and 3-State pins.
The primary global clock inputs (PGCK1-PGCK4) are
taken directly from the pins, and cannot be overwritten with
boundary-scan data. However, if necessary, it is possible to
drive the clock input from boundary scan. The external
clock source is 3-stated, and the clock net is driven with
boundary scan data through the output driver in the
clock-pad IOB. If the clock-pad IOBs are used for non-clock
signals, the data may be overwritten normally.
The data register also includes the following non-pin bits:
TDO.T, and TDO.O, which are always bits 0 and 1 of the
data register, respectively, and BSCANT.UPD, which is
always the last bit of the data register. These three bound-
ary scan bits are special-purpose Xilinx test signals.
The other standard data register is the single flip-flop
BYPASS register. It synchronizes data being passed
through the FPGA to the next downstream boundary scan
device.
Pull-up and pull-down resistors remain active during
boundary scan. Before and during configuration, all pins
are pulled up. After configuration, the choice of internal
pull-up or pull-down resistor must be taken into account
when designing test vectors to detect open-circuit PC
traces.
The FPGA provides two additional data registers that can
be specified using the BSCAN macro. The FPGA provides
two user pins (BSCAN.SEL1 and BSCAN.SEL2) which are
the decodes of two user instructions, USER1 and USER2.
For these instructions, two corresponding pins
(BSCAN.TDO1 and BSCAN.TDO2) allow user scan data to
From a cavity-up view of the chip (as shown in XDE or
Epic), starting in the upper right chip corner, the boundary
scan data-register bits are ordered as shown in Table 8.
The device-specific pinout tables for the XC5200 Series
include the boundary scan locations for each IOB pin.
be shifted out on TDO.
The data register clock
(BSCAN.DRCK) is available for control of test logic which
the user may wish to implement with CLBs. The NAND of
TCK and RUN-TEST-IDLE is also provided (BSCAN.IDLE).
Table 8: Boundary Scan Bit Sequence
Bit Position
I/O Pad Location
Top-edge I/O pads (right to left)
...
Instruction Set
Bit 0 (TDO)
The XC5200-Series boundary scan instruction set also
includes instructions to configure the device and read back
the configuration data. The instruction set is coded as
shown in Table 7.
Bit 1
...
Left-edge I/O pads (top to bottom)
Bottom-edge I/O pads (left to right)
Right-edge I/O pads (bottom to top)
BSCANT.UPD
...
...
Table 7: Boundary Scan Instructions
Bit N (TDI)
Instruction I2
I1 I0
Test
Selected
I/O Data
Source
TDO Source
BSDL (Boundary Scan Description Language) files for
XC5200-Series devices are available on the Xilinx web site
in the File Download area.
0
0
0
0
0
1
EXTEST
DR
DR
DR
SAMPLE/PR
ELOAD
Pin/Logic
Including Boundary Scan
0
0
1
1
1
0
0
1
0
USER 1
BSCAN.
TDO1
User Logic
User Logic
Pin/Logic
If boundary scan is only to be used during configuration, no
special elements need be included in the schematic or HDL
code. In this case, the special boundary scan pins TDI,
TMS, TCK and TDO can be used for user functions after
configuration.
USER 2
BSCAN.
TDO2
READBACK Readback
Data
To indicate that boundary scan remain enabled after config-
uration, include the BSCAN library symbol and connect pad
symbols to the TDI, TMS, TCK and TDO pins, as shown in
Figure 20.
1
1
1
0
1
1
1
0
1
CONFIGURE
Reserved
DOUT
Disabled
—
—
—
BYPASS
Bypass
Register
7-100
November 5, 1998 (Version 5.2)
ETC [ ETC ]
