R
XC4000E and XC4000X Series Field Programmable Gate Arrays
6-44
May 14, 1999 (Version 1.6)
Instruction Set
The XC4000 Series boundary scan instruction set also
includes instructions to congure the device and read back
the conguration data. The instruction set is coded as
Bit Sequence
The bit sequence within each IOB is: In, Out, 3-State. The
input-only M0 and M2 mode pins contribute only the In bit
to the boundary scan I/O data register, while the out-
put-only M1 pin contributes all three bits.
The rst two bits in the I/O data register are TDO.T and
TDO.O, which can be used for the capture of internal sig-
nals. The nal bit is BSCANT.UPD, which can be used to
drive an internal net. These locations are primarily used by
Xilinx for internal testing.
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
Figure 42.The device-specic pinout tables for the XC4000 Series
include the boundary scan locations for each IOB pin.
BSDL (Boundary Scan Description Language) les for
XC4000 Series devices are available on the Xilinx FTP site.
Including Boundary Scan in a Schematic
If boundary scan is only to be used during conguration, no
special schematic elements need be included in the sche-
matic or HDL code. In this case, the special boundary scan
pins TDI, TMS, TCK and TDO can be used for user func-
tions after conguration.
To indicate that boundary scan remain enabled after cong-
uration, place the BSCAN library symbol and connect the
TDI, TMS, TCK and TDO pad symbols to the appropriate
Even if the boundary scan symbol is used in a schematic,
the input pins TMS, TCK, and TDI can still be used as
inputs to be routed to internal logic. Care must be taken not
to force the chip into an undesired boundary scan state by
inadvertently applying boundary scan input patterns to
these pins. The simplest way to prevent this is to keep TMS
High, and then apply whatever signal is desired to TDI and
TCK.
D
Q
D
Q
IOB
M
U
X
BYPASS
REGISTER
IOB
TDO
TDI
IOB
1
0
1
0
1
0
1
0
1
0
sd
LE
DQ
D
Q
D
Q
1
0
1
0
1
0
1
0
DQ
LE
sd
LE
DQ
sd
LE
DQ
IOB
D
Q
1
0
DQ
LE
sd
IOB.T
DATA IN
IOB.I
IOB.Q
IOB.T
IOB.I
SHIFT/
CAPTURE
CLOCK DATA
REGISTER
DATAOUT
UPDATE
EXTEST
X9016
INSTRUCTION REGISTER
Figure 41: XC4000 Series Boundary Scan Logic
Product Obsolete or Under Obsolescence