SN74ACT7806

256

× 18

STROBED FIRST-IN, FIRST-OUT MEMORY

SCAS438C – APRIL 1992 – 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

Location 1

Location 2

Location 255

Location 256

256

× 18 SRAM

Write

Pointer

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 AF/AE, or the default value

of 32 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,

12–14

I

18-bit data input port

EMPTY

29

O

Empty flag. EMPTY is high when the FIFO memory is not empty; EMPTY is low when the FIFO memory

is empty or upon assertion of RESET.

FULL

28

O

Full flag. FULL is high when the FIFO memory is not full or upon assertion of RESET; FULL is low when

the FIFO memory is full.

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–D6

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 this input resets the FIFO and drives 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.