OR4 datasheet(10/152 Pages) LATTICE

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Lattice Semiconductor

Data Sheet

May, 2006

ORCA Series 4 FPGAs

Programmable Logic Cells (continued)

Look-Up Table Operating Modes

The operating mode affects the functionality of the PFU input and output ports and internal PFU routing. For exam-

ple, in some operating modes, the DIN[7:0] inputs are direct data inputs to the PFU latches/FFs. In memory mode,

the same DIN[7:0] inputs are used as a 4-bit write data input bus and a 4-bit write address input bus into LUT

memory.

Table 2 lists the basic operating modes of the LUT. Figure 4—Figure 7 show block diagrams of the LUT operating

modes. The accompanying descriptions demonstrate each mode’s use for generating logic.

Table 2. Look-Up Table Operating Modes

PFU Control Inputs

Each PFU has eight routable control inputs and an active-low, asynchronous global set/reset (GSRN) signal that

affects all latches and FFs in the device. The eight control inputs are CLK[1:0], LSR[1:0], CE[1:0], and SEL[1:0],

and their functionality for each logic mode of the PFU is shown in Table 3. The clock signal to the PFU is CLK, CE

stands for clock enable, which is its primary function. LSR is the local set/reset signal that can be conﬁgured as

synchronous or asynchronous. The selection of set or reset is made for each latch/FF and is not a function of the

signal itself. SEL is used to dynamically select between direct PFU input and LUT output data as the input to

the latches/FFs.

All of the control signals can be disabled and/or inverted via the conﬁguration logic. A disabled clock enable

indicates that the clock is always enabled. A disabled LSR indicates that the latch/FF never sets/resets (except

from GSRN). A disabled SEL input indicates that DIN[7:0] PFU inputs are routed to the latches/FFs.

Table 3. Control Input Functionality

Mode

Function

Logic

4-, 5-, and 6-input LUTs; softwired LUTs; latches/FFs with direct input or LUT input; CIN as direct

input to ninth FF or as pass through to COUT.

Half Logic/

Half Ripple

Upper four LUTs and latches/FFs in logic mode; lower four LUTs and latches/FFs in ripple mode;

CIN and ninth FF for logic or ripple functions.

Ripple

All LUTs combined to perform ripple-through data functions. Eight LUT registers available for

direct-in use or to register ripple output. Ninth FF dedicated to ripple out, if used. The submodes of

ripple mode are adder/subtractor, counter, multiplier, and comparator.

Memory

All LUTs and latches/FFs used to create a 32x4 synchronous dual-port RAM. Can be used as

single-port or as ROM.

Mode

CLK

[1:0]

LSR

[1:0]

SEL

[1:0]

Logic

CLK to all latches/

FFs

LSR to all latches/FFs,

enabled per nibble and

for ninth FF

CE to all latches/FFs,

selectable per nibble

and for ninth FF

Select between LUT

input and direct input for

eight latches/FFs

Half Logic/

Half Ripple

CLK to all latches/

FFs

LSR to all latches/FF,

enabled per nibble and

for ninth FF

CE to all latches/FFs,

selectable per nibble

and for ninth FF

Select between LUT

input and direct input for

eight latches/FFs

Ripple

CLK to all latches/

FFs

LSR to all latches/FFs,

enabled per nibble and

for ninth FF

CE to all latches/FFs,

selectable per nibble

and for ninth FF

Select between LUT

input and direct input for

eight latches/FFs

Memory

(RAM)

CLK to RAM

LSR0 Port enable 2

CE1 RAM write enable

CE0 Port enable 1

Not used

Memory

(ROM)

Optional for

synchronous outputs

Not used

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