OR2C04A datasheet(15/192 Pages) ETC

15 / 192 page

Lucent Technologies Inc.

Data Sheet

June 1999

ORCA Series 2 FPGAs

Programmable Logic Cells (continued)

5-4641(F).r1

Figure 17. SDPM Mode—16 x 2 Synchronous

Dual-Port Memory

The Series 2 devices have added a second synchro-

nous memory mode known as the synchronous dual-

port memory (SDPM) mode. This mode writes data

into the memory synchronously in the same manner

described previously for SSPM mode. The SDPM

mode differs in that two separate 16 x 2 memories are

created in each PFU that have the same WE, WPE,

write data (WD[1:0]), and write address (WA[3:0])

inputs, as shown in Figure 17.

The outputs of HLUTA (F[3:2]) operate the same way

they do in SSPM mode—the read address comes

directly from the A[3:0] inputs used to create the

latched write address. The outputs of HLUTB (F[1:0])

operate in a dual-port mode where the write address

comes from the latched version of A[3:0], and the read

address comes directly from RA[3:0], which is input on

B[3:0].

Since external multiplexing of the write address and

read address is not required, extremely fast RAMs can

be created. New system applications that require an

interface between two different asynchronous clocks

can also be implemented using the SDPM mode. An

example of this is accomplished by creating FIFOs

where one clock controls the synchronous write of data

into the FIFO, and the other clock controls the read

address to allow reading of data at any time from the

FIFO.

Latches/Flip-Flops

The four latches/FFs in the PFU can be used in a vari-

ety of configurations. In some cases, the configuration

options apply to all four latches/FFs in the PFU. For

other options, each latch/FF is independently program-

mable.

Table 4 summarizes these latch/FF options. The

latches/FFs can be configured as either positive or

negative level-sensitive latches, or positive or negative

edge-triggered flip-flops. All latches/FFs in a given PFU

share the same clock, and the clock to these latches/

FFs can be inverted. The input into each latch/FF is

from either the corresponding QLUT output (F[3:0]) or

the direct data input (WD[3:0]). For latches/FFs located

in the two outer rings of PLCs, additional inputs are

possible. These additional inputs are fast paths from

I/O pads located in PICs in the same row or column as

the PLCs. If the latch/FF is not located in the two outer

rings of the PLCs, the latch/FF input can also be tied to

logic 0, which is the default. The four latch/FF outputs,

Q[3:0], can be placed on the five PFU outputs, O[4:0].

Table 4. Configuration RAM Controlled Latch/

Flip-Flop Operation

The four latches/FFs in a PFU share the clock (CK),

clock enable (CE), and local set/reset (LSR) inputs.

When CE is disabled, each latch/FF retains its previous

value when clocked. Both the clock enable and LSR

inputs can be inverted to be active-low.

WPE

CIN, C0

WA[3:0]

WD[1:0]

WA[3:0]

RA[3:0]

WD[1:0]

HLUTA

WA[3:0]

RA[3:0]

WD[1:0]

HLUTB

WRITE PULSE

GENERATOR

A[3:0]

WD[1:0]

RA[3:0] B[3:0]

Function

Options

Functionality Common to All Latch/FFs in PFU

LSR Operation

Asynchronous or synchronous

Clock Polarity

Noninverted or inverted

Front-End Select

Direct (WD[3:0]) or from LUT

(F[3:0])

LSR Priority

Either LSR or CE has priority

Functionality Set Individually in Each Latch/FF in PFU

Latch/FF Mode

Latch or flip-flop

Set/Reset Mode

Set or Reset

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