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OR2T06A-3BC84I View Datasheet(PDF) - Unspecified

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OR2T06A-3BC84I Datasheet PDF : 192 Pages
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Data Sheet
June 1999
ORCA Series 2 FPGAs
Programmable Logic Cells (continued)
Table 3 lists the basic operating modes of the LUT. The
operating mode affects the functionality of the PFU
input and output ports and internal PFU routing. For
example, in some operating modes, the WD[3:0] inputs
are direct data inputs to the PFU latches/FFs. In the
dual 16 x 2 memory mode, the same WD[3:0] inputs
are used as a 4-bit data input bus into LUT memory.
The PFU is used in a variety of modes, as illustrated in
Figures 4 through 11, and it is these specific modes
that are most relevant to PFU functionality.
PFU Control Inputs
The four control inputs to the PFU are clock (CK), local
set/reset (LSR), clock enable (CE), and C0. The CK,
CE, and LSR inputs control the operation of all four
latches in the PFU. An active-low global set/reset
(GSRN) signal is also available to the latches/FFs in
every PFU. Their operation is discussed briefly here,
and in more detail in the Latches/Flip-Flops section.
The polarity of the control inputs can be inverted.
The CK input is distributed to each PFU from a vertical
or horizontal net. The CE input inhibits the latches/FFs
from responding to data inputs. The CE input can be
disabled, always enabling the clock. Each latch/FF can
be independently programmed to be set or reset by the
LSR and the global set/reset (GSRN) signals. Each
PFU’s LSR input can be configured as synchronous or
asynchronous. The GSRN signal is always asynchro-
nous. The LSR signal applies to all four latches/FFs in
a PFU. The LSR input can be disabled (the default).
The asynchronous set/reset is dominant over clocked
The C0 input is used as an input into the special PFU
gates for wide functions in combinatorial logic mode.
In the memory modes, this input is also used as the
write-port enable input. The C0 input can be disabled
(the default).
used as LUT inputs. The use of these ports changes
based on the PFU operating mode.
The functionality of the LUT is determined by its operat-
ing mode. The entries in Table 3 show the basic modes
of operation for combinatorial logic, ripple, and memory
functions in the LUT. Depending on the operating
mode, the LUT can be divided into sub-LUTs. The LUT
is comprised of two 32-bit half look-up tables, HLUTA
and HLUTB. Each half look-up table (HLUT) is com-
prised of two quarter look-up tables (QLUTs). HLUTA
consists of QLUT2 and QLUT3, while HLUTB consists
of QLUT0 and QLUT1. The outputs of QLUT0, QLUT1,
QLUT2, and QLUT3 are F0, F1, F2, and F3, respec-
Table 3. Look-Up Table Operating Modes
F4A Two functions of four inputs, some inputs
shared (QLUT2/QLUT3)
F4B Two functions of four inputs, some inputs
shared (QLUT0/QLUT1)
F5A One function of five inputs (HLUTA)
F5B One function of five inputs (HLUTB)
R 4-bit ripple (LUT)
MA 16 x 2 asynchronous memory (HLUTA)
MB 16 x 2 asynchronous memory (HLUTB)
SSPM 16 x 4 synchronous single-port memory
SDPM 16 x 2 synchronous dual-port memory
For combinatorial logic, the LUT can be used to do any
single function of six inputs, any two functions of five
inputs, or four functions of four inputs (with some inputs
shared), and three special functions based on the two
five-input functions and C0.
Look-Up Table Operating Modes
The look-up table (LUT) can be configured to operate
in one of three general modes:
s Combinatorial logic mode
s Ripple mode
s Memory mode
The combinatorial logic mode uses a 64-bit look-up
table to implement Boolean functions. The two 5-bit
logic inputs, A[4:0] and B[4:0], and the C0 input are
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