LH540235 datasheet(6/46 Pages) SHARP

Part #	LH540235

Description	2048 x 18 / 4096 x 18 Synchronous FIFOs

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Manufacturer	SHARP [Sharp Corporation]

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PIN DESCRIPTIONS

NAME

TYPE

1

DESCRIPTION

D0 – D17

Data Inputs

I

Data inputs from an 18-bit bus.

RS

Reset

I

When RS is taken LOW, the FIFO’s internal read and write pointers are set to

address the first physical location of the RAM array; FF, PAF, and HF go HIGH;

and PAE and EF go LOW. The programmable-flag-offset registers

and the

Control Register are set to their default values. (But see the description of

EMODE, below.) A reset operation is required before an initial read or write

operation after power-up.

EMODE

Enhanced

Operating

Mode

I

When EMODE is tied LOW, the default setting for Control Register bits 00-

05 after a reset operation changes to HIGH rather than LOW, thus enabling

all Control-Register-controllable Enhanced Operating Mode features, and

allowing access to the Control Register for reprogramming or readback

(see Tables 1, 2, and 5). If this behavior is desired, EMODE may be

grounded; however, Control Register bits 00-06 still may be individually

programmed to selectively enable or disable certain of the Enhanced Mode

features, even though those features associated with interlocked-paralleled

operation always are enabled whenever EMODE is being asserted (see

Table 2). Alternatively, EMODE may be tied to VCC, so that the FIFO is

functionally IDT-compatible, and the Control Register is not accessible or

visible, and all of its bits remain LOW. Controlling EMODE dynamically

during system operation is not recommended.

WCLK

Write Clock

I

Data is written into the FIFO on a LOW-to-HIGH transition of WCLK, whenever

WEN (Write Enable) is being asserted (LOW), and LD is HIGH. If LD is LOW, a

programmable register rather than the internal FIFO memory is written into.

In

the Enhanced Operating Mode, whenever Control Register bit 06 is HIGH,

WEN2 is ANDed with WEN to produce an effective internal write-enable

signal.

2

WEN

Write Enable

I

When WEN is LOW and LD is HIGH, an 18-bit data word is written into the FIFO

on every LOW-to-HIGH transition of WCLK. When WEN is HIGH, the FIFO

internal memory continues to hold the previous data (see Table 3). Data will not

be written into the FIFO if FF is LOW.

In the Enhanced Operating Mode,

whenever Control Register bit 06 is HIGH, WEN2 is ANDed with WEN to

produce an effective internal write-enable signal.

2

RCLK

Read Clock

I

Data is read from the FIFO on a LOW-to-HIGH transition of RCLK whenever

REN (Read Enable) is being asserted (LOW), and LD is HIGH. If LD is LOW, a

programmable register rather than the internal FIFO memory is read from.

In the

Enhanced Operating Mode, whenever Control Register bit 06 is HIGH, REN2

is ANDed with REN (and whenever Control Register bit 05 is HIGH, also

with OE) to produce an effective internal read-enable signal.

2

REN

Read Enable

I

When REN is LOW and LD is HIGH, an 18-bit data word is read from the FIFO

on every LOW-to-HIGH transition of RCLK. When REN is HIGH, and/or also

when EF is LOW, the FIFO’s output register continues to hold the previous data

word, whether or not Q0 – Q17 (the data outputs) are enabled (see Table 3). In

the Enhanced Operating Mode, whenever Control Register bit 06 is HIGH,

REN2 is ANDed with REN (and whenever Control Register bit 05 is HIGH,

also with OE) to produce an effective internal read-enable signal.

2

OE

Output Enable

I

When OE is LOW, the FIFO’s data outputs drive the bus to which they are

connected. If OE is HIGH, the FIFO’s outputs are in high-Z (high-impedance)

state.

In the Enhanced Operating Mode, OE not only continues to control

the outputs in this same manner, but also can function as an additional

ANDing input to the combined effective read-enable signal, along with REN

and REN2, whenever Control Register bit 05 is HIGH (see Table 5).

2

BOLD ITALIC = Enhanced Operating Mode

LH540235/45

2048 x 18/4096 x 18 Synchronous FIFOs

6

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