SN74ACT7808

2048

× 9 STROBED FIRST-IN, FIRST-OUT MEMORY

SCAS205D – FEBRUARY 1991 – REVISED APRIL 1998

13

POST OFFICE BOX 655303

APPLICATION INFORMATION

depth cascading (see Figure 7)

The SN74ACT7808 provides expansion logic necessary for cascading an unlimited number of the FIFOs in

depth. CASEN must be low on all FIFOs used in depth expansion. FL must be tied low on the first FIFO in the

chain; all others must have FL tied high. The expansion-out (XO) output of a FIFO must be tied to the

expansion-in (XI) input of the next FIFO in the chain. The XO output of the last FIFO is tied to the XI input of

the first FIFO to complete the loop. Data buses are common to each FIFO in the chain. A composite EMPTY

and FULL signal must be generated to indicate boundary conditions.

Q0–Q8

XI

XO

RESET

D0–D8

LDCK

UNCK

CASEN

FULL EMPTY

FL

OE

SN74ACT7808

L

L

RESET

OE

Q0–Q8

UNCK

EMPTY

FULL

LDCK

D0–D8

XI

XO

RESET

Q0–Q8

LDCK

UNCK

CASEN

FULL EMPTY

FL

OE

SN74ACT7808

L

H

XI

XO

RESET

Q0–Q8

LDCK

UNCK

CASEN

FULL EMPTY

FL

OE

SN74ACT7808

L

H

D0–D8

D0–D8

9

9

9

9

9

9

9

9

Figure 7. Depth Cascading to Form a 6K

× 9 FIFO