R
May 14, 1999 (Version 1.6)
6-55
XC4000E and XC4000X Series Field Programmable Gate Arrays
6
Readback
The user can read back the content of conguration mem-
ory and the level of certain internal nodes without interfer-
ing with the normal operation of the device.
Readback not only reports the downloaded conguration
bits, but can also include the present state of the device,
represented by the content of all ip-ops and latches in
CLBs and IOBs, as well as the content of function genera-
tors used as RAMs.
Note that in XC4000 Series devices, conguration data is
not inverted with respect to conguration as it is in XC2000
and XC3000 families.
XC4000 Series Readback does not use any dedicated
pins, but uses four internal nets (RDBK.TRIG, RDBK.DATA,
RDBK.RIP and RDBK.CLK) that can be routed to any IOB.
To access the internal Readback signals, place the READ-
BACK library symbol and attach the appropriate pad sym-
After Readback has been initiated by a High level on
RDBK.TRIG after conguration, the RDBK.RIP (Read In
Progress) output goes High on the next rising edge of
RDBK.CLK. Subsequent rising edges of this clock shift out
Readback data on the RDBK.DATA net.
Readback data does not include the preamble, but starts
with ve dummy bits (all High) followed by the Start bit
(Low) of the rst frame. The rst two data bits of the rst
frame are always High.
Each frame ends with four error check bits. They are read
back as High. The last seven bits of the last frame are also
read back as High. An additional Start bit (Low) and an
11-bit Cyclic Redundancy Check (CRC) signature follow,
before RDBK.RIP returns Low.
DONE
*
**
QS
R
1
0
1
0
1
0
1
0
1
GSR ENABLE
GSR INVERT
STARTUP.GSR
STARTUP.GTS
GTS INVERT
GTS ENABLE
CONTROLLED BY STARTUP SYMBOL
IN THE USER SCHEMATIC (SEE
LIBRARIES GUIDE)
GLOBAL SET/RESET OF
ALL CLB AND IOB FLIP-FLOP
IOBs OPERATIONAL PER CONFIGURATION
GLOBAL 3-STATE OF ALL IOBs
Q2
Q3
Q1/Q4
DONE
IN
STARTUP
Q0
Q1
Q2
Q3
Q4
M
" FINISHED "
ENABLES BOUNDARY
SCAN, READBACK AND
CONTROLS THE OSCILLATOR
K
SQ
K
DQ
K
DQ
K
DQ
K
DQ
FULL
LENGTH COUNT
CLEAR MEMORY
CCLK
STARTUP.CLK
USER NET
CONFIGURATION BIT OPTIONS SELECTED BY USER IN "MAKEBITS"
X1528
Figure 48: Start-up Logic
Product Obsolete or Under Obsolescence