R
XC4000E and XC4000X Series Field Programmable Gate Arrays
For actual timing values please refer to “Configuration
Switching Characteristics” on page 68. Be sure that the
serial PROM and slaves are fast enough to support this
data rate. XC2000, XC3000/A, and XC3100A devices do
not support the Fast ConfigRate option.
Master Serial Mode
In Master Serial mode, the CCLK output of the lead FPGA
drives a Xilinx Serial PROM that feeds the FPGA DIN input.
Each rising edge of the CCLK output increments the Serial
PROM internal address counter. The next data bit is put on
the SPROM data output, connected to the FPGA DIN pin.
The lead FPGA accepts this data on the subsequent rising
CCLK edge.
The SPROM CE input can be driven from either LDC or
DONE. Using LDC avoids potential contention on the DIN
pin, if this pin is configured as user-I/O, but LDC is then
restricted to be a permanently High user output after con-
figuration. Using DONE can also avoid contention on DIN,
provided the early DONE option is invoked.
The lead FPGA then presents the preamble data—and all
data that overflows the lead device—on its DOUT pin.
There is an internal pipeline delay of 1.5 CCLK periods,
which means that DOUT changes on the falling CCLK
edge, and the next FPGA in the daisy chain accepts data
on the subsequent rising CCLK edge.
Figure 51 on page 60 shows a full master/slave system.
The leftmost device is in Master Serial mode.
Master Serial mode is selected by a <000> on the mode
pins (M2, M1, M0).
In the bitstream generation software, the user can specify
Fast ConfigRate, which, starting several bits into the first
frame, increases the CCLK frequency by a factor of eight.
CCLK
(Output)
T
2
CKDS
T
DSCK
1
6
Serial Data In
n
n + 1
n + 2
Serial DOUT
(Output)
n – 3
n – 2
n – 1
n
X3223
Description
DIN setup
DIN hold
Symbol
TDSCK
TCKDS
Min
20
0
Max
Units
ns
1
CCLK
2
ns
Notes: 1. At power-up, Vcc must rise from 2.0 V to Vcc min in less than 25 ms, otherwise delay configuration by pulling PROGRAM
Low until Vcc is valid.
2. Master Serial mode timing is based on testing in slave mode.
Figure 53: Master Serial Mode Programming Switching Characteristics
May 14, 1999 (Version 1.6)
6-61
XILINX [ XILINX, INC ]
