SN74ALVC7806

256

× 18

LOW-POWER FIRST-IN, FIRST-OUT MEMORY

SCAS591A – OCTOBER 1997 – REVISED APRIL 1998

3

POST OFFICE BOX 655303

functional block diagram

Q0–Q17

AF/AE

HF

OE

D0–D17

UNCK

LDCK

RESET

PEN

EMPTY

FULL

Status-

Flag

Logic

Read

Pointer

Reset

Logic

256

× 18

Write

Pointer

RAM

Terminal Functions

TERMINAL

I/O

DESCRIPTION

NAME

NO.

I/O

DESCRIPTION

AF/AE

24

O

Almost full/almost empty flag. Depth-offset values can be programmed for this flag or the default value

of 64 can be used for both the almost empty offset (X) and the almost full offset (Y). AF/AE is high when

memory contains X or fewer words or (256 – Y) or more words. AF/AE is high after reset.

D0–D17

2–9, 11–12,

14–21

I

18-bit data input port

EMPTY

29

O

Empty flag. EMPTY is low when the FIFO is empty. A FIFO reset also causes EMPTY to go low.

FULL

28

O

Full flag. FULL is low when the FIFO is full. A FIFO reset causes FULL to go high.

HF

22

O

Half-full flag. HF is high when the FIFO memory contains 128 or more words. HF is low after reset.

LDCK

25

I

Load clock. Data is written to the FIFO on the rising edge of LDCK when FULL is high.

OE

56

I

Output enable. When OE is high, the data outputs are in the high-impedance state.

PEN

23

I

Program enable. After reset and before the first word is written to the FIFO, the binary value on D0–D7

is latched as an AF/AE offset value when PEN is low and WRTCLK is high.

Q0–Q17

33–34, 36–38,

40–43, 45–49,

51, 53–55

O

18-bit data output port

RESET

1

I

Reset. A low level on RESET resets the FIFO and drives AF/AE and FULL high and HF and EMPTY low.

UNCK

32

I

Unload clock. Data is read from the FIFO on the rising edge of UNCK when EMPTY is high.