Data Sheet
ATT3000 Series Field-Programmable Gate Arrays
February 1997
4
Lucent Technologies Inc.
Configuration Memory
The static memory cell used for the configuration mem-
ory in the FPGA has been designed specifically for
high reliability and noise immunity. Integrity of the
FPGA configuration memory based on this design is
ensured even under various adverse conditions. Com-
pared with other programming alternatives, static mem-
ory is believed to provide the best combination of high
density, high performance, high reliability, and compre-
hensive testability.
As shown in Figure 2, the basic memory cell consists of
two CMOS inverters plus a pass transistor used for
writing and reading cell data. The cell is only written to
during configuration and only read from during read-
back. During normal operation, the cell provides contin-
uous control and the pass transistor is off and does not
affect cell stability. This is quite different from the opera-
tion of conventional memory devices, in which the cells
are frequently read and rewritten.
The memory cell outputs Q and Q use full ground and
VCC levels and provide continuous, direct control. The
additional capacitive load and the absence of address
decoding and sense amplifiers provide high stability to
the cell. Due to their structure, the configuration mem-
ory cells are not affected by extreme power supply
excursions or very high levels of alpha particle radia-
tion. Soft errors have not been observed in reliability
testing.
Two methods of loading configuration data use serial
data, while three use byte-wide data. The internal con-
figuration logic utilizes framing information, embedded
in the program data by the ORCA Foundry Develop-
ment System, to direct memory cell loading. The serial
data framing and length count preamble provide pro-
gramming compatibility for mixes of various Lucent pro-
grammable gate arrays in a synchronous, serial, daisy-
chain fashion.
Figure 2. Static Configuration Memory Cell
READ OR
WRITE
DATA
Q
Q
CONFIGURATION
CONTROL
5-3101(F)
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