OPERATIONAL MODES

Standalone Configuration

When depth cascading is not required for a given

application, the LH540203 is placed in standalone mode

by tying the Expansion In input (XI) to ground. This

input is internally sampled during a reset operation. (See

Table 1.)

Width Expansion

Word-width expansion is implemented by placing mul-

tiple LH540203 devices in parallel. Each LH540203

should be configured for standalone mode. In this ar-

rangement, the behavior of the status flags is identical for

all devices; so, in principle, a representative value for

each of these flags could be derived from any one device.

In practice, it is better to derive ‘composite’ flag values

using external logic, since there may be minor speed

variations between different actual devices. (See Figures

4, 5, and 6.)

WRITE

DATA IN

9

FULL FLAG

RESET

XI

RT

RETRANSMIT

EMPTY FLAG

9

READ

HF

LH540203

W

FF

RS

R

EF

DATA OUT

540203-17

Figure 4. Standalone FIFO (2048

× 9)

18

WRITE

FULL FLAG

RESET

9

READ

EMPTY FLAG

R

EF

XI

RT

R

W

540203-18

RS

RETRANSMIT

RT

XI

HF

W

FF

RS

9

18

9

HF

9

LH540203

LH540203

DATA IN

DATA OUT

Figure 5. FIFO Word-Width Expansion (2048

× 18)

CMOS 2048

× 9 Asynchronous FIFO

LH540203

5