Spar tan and Spar tan -XL Families Field Programm able Gate Arrays
20 www.xilinx.com DS060 (v1.6) S eptember 19, 2001
1-800-255-7778 Product Specification
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On-Chip Oscillator
Spartan/XL devices include an internal oscillator . This oscil-
lator is used to clock the power-on time-out, for configura-
tion memory clearing, and as the source of CCLK in Master
configuration mode. The oscillator runs at a nominal 8 MHz
frequency that varies with process, VCC, and temperature.
The output frequency fal ls between 4 MHz and 10 MHz.
The oscillator output is optionally available after configura-
tion. An y t wo of four resynchronized taps of a built-in divider
are also available. These taps are at the four th, ninth, fou r-
teenth and nineteenth bits of the divider. Therefore, if the
primary oscillator output is running at the nominal 8 MHz,
the user has access to an 8-MHz clock, plus any two of
500 kHz, 16 kHz, 490 Hz and 15 Hz. These frequencies
can vary by as much as -50% or +2 5% .
These signals can be accessed by placing the OSC4 library
element in a schematic or in HDL code. The oscillator is
automatically disabled after con figuration if the OSC 4 sy m-
bol is not used in th e design.
Global S ignals: GSR and GTS
Global Set/Reset
A separate Global Set/Reset line, as shown in Figure 3,
page 5 for t he CLB and Figure 5, page 6 f or the IOB, sets or
clears each flip-flop during power-up, reconfiguration, or
when a dedicated Reset net is driven activ e. This global net
(GSR) does not compete with other routing resources; it
uses a dedicated distribution network.
Each flip-flop is configured as either globally set or reset in
the same way that the local set/reset (SR) is specified.
Therefore, if a flip-flop is set by SR, it is also set by GSR.
Similar ly, if in reset mode, it is reset by bot h SR and GSR.
GSR can be driven from any user-programmable pin as a
global reset input. To use this global net, place an input pad
and input buffer in the sche matic o r HDL code, driving the
GSR pi n of the STARTUP symbol. (See Figure 19.) A spe-
cific pin lo cation can be assigned to this input using a LOC
attribute or property, just as with any other user-program-
mable pad. An inver ter can optiona lly be inser ted after the
input buffer to invert the sen se of the G SR signal. A lterna-
tive ly, GS R can be dr iven from any inter nal node.
Global 3-State
A separate Global 3-state line (GTS) as shown in Figure 6,
page 7 forces all FPGA outputs to the high-impedance
state, unless b oundary scan is enabled and is executing an
EXTEST instruction. GTS does not compete with other rout-
ing resources; it uses a dedicated distribution network.
GTS can be driven from any user-programmable pin as a
global 3-state input. To use this global net, place an input
pad and inp ut buffer in the schemat ic or HDL code, dr iving
the GTS pin of the STAR TUP symbol. This is similar to what
is shown in Figure 19 for GSR except the IBUF would be
conn ected to GTS. A s pecific pin locat ion can be ass igned
to this input using a LOC attribute or property, j ust as with
any other user-programmable pad. An inverter can option-
ally be inser ted after the input buffer to inver t the sense of
the Global 3-state signal. Alternatively, GTS can be driven
from any internal node.
Boundary Scan
The "bed of nails" has been the traditional method of testing
electronic assemblies. This approach has become less
appropriate, due to closer pin spacing and more sophisti-
cated assembly methods like surface-mount technology
and multi-la yer boards. The IEEE Boundary Scan Standard
1149.1 was developed to facilitate board-level testing of
electronic assemblies. Design and test engineers can
embed a standard test logic structure in their device to
achieve high fault coverage for I/O and internal logic. This
struct ure is easil y implemented with a four-pin interface on
any boundary scan compatible device. IEEE 1149.1-com-
patible devices may be serial daisy-chained together, con-
nected in parallel, or a combina tion of the two.
The Spartan and Spartan-XL families implement IEEE
1149.1-compatible BYPASS, PRELOAD/SAMPLE and
EXTE ST boundar y scan instructions. When the boundar y
scan configuratio n option is se lecte d, three norm al user I/O
pins become dedicated inputs for these functions. Another
user output pin becom es the dedicated boun dary scan out-
put. The details of how to enable this circuitry are covered
l a te r i n thi s se ct i o n .
By exercising these input sig nals, the user can ser ially load
commands and data into these devices to control the driving
of thei r out put s and to examine thei r inpu ts. This m et hod is
an improv ement over bed-of- nails testing. It a voids the need
to over-drive device outputs, and it reduces the user inter-
face to four pins. An opt ional fifth pin, a reset for the control
logic, is described in the standard but is not implemented in
the Spart an/X L devices .
The dedicated on-c hip logic implem ent ing the IE E E 1 149.1
functions in cludes a 1 6-state m ac hine, an in stru ction regis-
ter and a number of data registers. The functional details
can be found in the IEEE 1149 .1 spec ification and are a lso
discu ssed in the Xilinx application note: "Bound ary S can in
FPGA Devi ce s."
Figure 19: S chema tic Symbo ls for G lobal Set/Reset
PAD
IBUF
GSR
GTS
CLK DONEIN
Q1, Q4
Q2
Q3
STARTUP
DS060_19_080400