24
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
NOTES:
1. Use an AND gate in IDT Standard mode, an OR gate in FWFT mode.
2. Do not connect any output control signals directly together.
3. FIFO #1 and FIFO #2 must be the same depth, but may be different word widths.
OPTIONAL CONFIGURATIONS
WIDTH EXPANSION CONFIGURATION
Word width may be increased simply by connecting together the
control signals of multiple devices. Status flags can be detected from
any one device. The exceptions are the EF and FF functions in IDT
Standard mode and the IR and OR functions in FWFT mode. Because
of variations in skew between RCLK and WCLK, it is possible for EF/FF
deassertion and IR/OR assertion to vary by one cycle between FIFOs. In
Figure 19. Block Diagram of 8,192 x 36 and 16,384 x 36 Width Expansion
IDT Standard mode, such problems can be avoided by creating compos-
ite flags, that is, ANDing EF of every FIFO, and separately ANDing FF of
every FIFO. In FWFT mode, composite flags can be created by ORing
OR of every FIFO, and separately ORing IR of every FIFO.
Figure 23 demonstrates a width expansion using two IDT72255LA/
72265LA devices. D0 - D17 from each device form a 36-bit wide input
bus and Q0-Q17 from each device form a 36-bit wide output bus. Any
word width can be attained by adding additional IDT72255LA/72265LA
devices.
WRITE CLOCK (WCLK)
m + n m n
MASTER RESET (
)
READ CLOCK (RCLK)
DATA OUT
n
m + n
WRITE ENABLE (
)
FULL FLAG/INPUT READY (
/ )
PROGRAMMABLE (
)
PROGRAMMABLE (
)
EMPTY FLAG/OUTPUT READY (
/ ) #2
OUTPUT ENABLE (
)
READ ENABLE (
)
m
LOAD (
)
IDT
72255LA
72265LA
EMPTY FLAG/OUTPUT READY ( / ) #1
PARTIAL RESET ( )
IDT
72255LA
72265LA
4670 drw 22
FULL FLAG/INPUT READY ( / ) #2
HALF-FULL FLAG (
)
FIRST WORD FALL THROUGH/
SERIAL INPUT (FWFT/SI)
RETRANSMIT (
)
#1
FIFO
#2
GATE
(1)
GATE
(1)
D
0
- Dm
DATA IN
Dm
+1
- Dn
Q
0
- Qm
Qm
+1
- Qn
FIFO
#1
