Lucent Technologies Inc.
21
Data Sheet
February 1997
ATT3000 Series Field-Programmable Gate Arrays
Configuration (continued)
The specific data format for each device is produced by
the bit stream generation program, and one or more of
these files can then be combined and appended to a
length count preamble and be transformed into a
PROM format file by the PROM generation program of
the ORCA Foundry Development System. The tie
option of the bit stream generation program defines
output levels of unused blocks of a design and con-
nects these to unused routing resources. This prevents
indeterminate levels which might produce parasitic
supply currents. This tie option can be omitted for quick
breadboard iterations where a few additional mA of ICC
are acceptable.
The configuration bit stream begins with high preamble
bits, a 4-bit preamble code, and a 24-bit length count.
When configuration is initiated, a counter in the FPGA
is set to 0 and begins to count the total number of con-
figuration clock cycles applied to the device. As each
configuration data frame is supplied to the FPGA, it is
internally assembled into a data word. As each data
word is completely assembled, it is loaded in parallel
into one word of the internal configuration memory
array. The configuration loading process is complete
when the current length count equals the loaded length
count and the required configuration program data
frames have been written. Internal user flip-flops are
held reset during configuration.
Two user-programmable pins are defined in the uncon-
figured FPGA: high during configuration (HDC) and low
during configuration (LDC), and DONE/PROG may be
used as external control signals during configuration. In
master mode configurations, it is convenient to use LDC
as an active-low EPROM chip enable. After the last
configuration data bit is loaded and the length count
compares, the user I/O pins become active. Options in
the bit stream generation program allow timing choices
of one clock earlier or later for the timing of the end of
the internal logic reset and the assertion of the DONE
signal. The open-drain DONE/PROG output can be
AND-tied with multiple FPGAs and used as an active-
high READY, an active-low PROM enable, or a RESET
to other portions of the system. The state diagram of
Figure 18 illustrates the configuration process.
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