7
COMMERCIAL TEMPERATURE RANGE
IDT7280/7281/7282/7283/7284/7285 5V ASYNCHRONOUS FIFO
DUAL 256 x 9, 512 x 9, 1,024 x 9, 2,048 x 9, 4,096 x 9 and 8,192 x 9
JUNE 29, 2012
Figure 9. Half-Full Flag Timing
Figure 10. Expansion Out
Figure 11. Expansion In
OPERATING MODES:
Care must be taken to assure that the appropriate flag is monitored by
each system (i.e. FF is monitored on the device where W is used; EF is monitored
on the device where R is used).
SINGLE DEVICE MODE
A single IDT7280/7281/7282/7283/7284/7285 may be used when the
application requirements are for 256/512/1,024/2,048/4,096/8,192 words or
less. These FIFOs are in a Single Device Configuration when the Expansion
In (XI) control input is grounded (see Figure 12).
DEPTH EXPANSION
These devices can easily be adapted to applications when the require-
ments are for greater than 256/512/1,024/2,048/4,096/8,192 words. Figure
14 demonstrates a four-FIFO Depth Expansion using two IDT7280/7281/
7282/7283/7284/7285s. Any depth can be attained by adding additional
IDT7280/7281/7282/7283/7284/7285s. These FIFOs operate in the Depth
Expansion mode when the following conditions are met:
1. The first FIFO must be designated by grounding the First Load (FL) control
input.
2. All other FIFOs must have FL in the HIGH state.
3. The Expansion Out (XO) pin of each device must be tied to the Expansion
In (XI) pin of the next device. See Figure 14.
4. External logic is needed to generate a composite Full Flag (FF) and Empty
Flag (EF). This requires the ORing of all EFs and ORing of all FFs (i.e. all
must be set to generate the correct composite FF or EF). See Figure 14.
5. The Retransmit (RT) function and Half-Full Flag (HF) are not available in
the Depth Expansion Mode.
R
W
HF
t
RHF
3208 drw 11
HALF-FULL OR LESS
MORE THAN HALF-FULL
HALF-FULL OR LESS
t
WHF
R
W
XO
3208 drw 12
WRITE TO
LAST PHYSICAL
LOCATION
t
XOL
t
XOH
READ FROM
LAST PHYSICAL
LOCATION
t
XOL
t
XOH
W
XI
R
3208 drw 13
WRITE TO
FIRST PHYSICAL
LOCATION
READ FROM
FIRST PHYSICAL
LOCATION
t
XIS
t
XIR
t
XI
t
XIS
8
COMMERCIAL TEMPERATURE RANGE
IDT7280/7281/7282/7283/7284/7285 5V ASYNCHRONOUS FIFO
DUAL 256 x 9, 512 x 9, 1,024 x 9, 2,048 x 9, 4,096 x 9 and 8,192 x 9
JUNE 29, 2012
Figure 13. Block Diagram of 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18, 4,096 x 18, 8,192 x 18 FIFO Memory Used in Width Expansion Mode
Figure 12. Block Diagram of One 256 x 9, 512 x 9, 1,024 x 9, 2,048 x 9, 4,096 x 9, 8,192 x 9 FIFO Used in Single Device Mode
USAGE MODES:
WIDTH EXPANSION
Word width may be increased simply by connecting the corresponding input
control signals of multiple FIFOs. Status flags (EF, FF and HF) can be detected
from any one FIFO. Figure 13 demonstrates an 18-bit word width by using the
two FIFOs contained in the IDT7280/7281/7282/7283/7284/7285s. Any word
width can be attained by adding FIFOs (Figure 13).
BIDIRECTIONAL OPERATION
Applications which require data buffering between two systems (each
system capable of Read and Write operations) can be achieved by pairing
IDT7280/7281/7282/7283/7384/7285s as shown in Figure 16. Both Depth
Expansion and Width Expansion may be used in this mode.
DATA FLOW-THROUGH
Two types of flow-through modes are permitted, a read flow-through
and write flow-through mode. For the read flow-through mode (Figure 17),
the FIFO permits a reading of a single word after writing one word of data into
an empty FIFO. The data is enabled on the bus in (t
WEF + tA) ns after the rising
edge of W, called the first write edge, and it remains on the bus until the R line
is raised from LOW-to-HIGH, after which the bus would go into a three-state
mode after tRHZ ns. The EF line would have a pulse showing temporary
deassertion and then would be asserted.
In the write flow-through mode (Figure 18), the FIFO permits the writing
of a single word of data immediately after reading one word of data from a
full FIFO. The R line causes the FF to be deasserted but the W line being LOW
causes it to be asserted again in anticipation of a new data word. On the rising
edge of W, the new word is loaded in the FIFO. The W line must be toggled when
FF is not asserted to write new data in the FIFO and to increment the write pointer.
COMPOUND EXPANSION
The two expansion techniques described above can be applied together
in a straightforward manner to achieve large FIFO arrays (see Figure 15).
WRITE (W)
DATA IN (D)
FULL FLAG (FF)
RESET (RS)
9
READ (R)
9
DATA OUT (Q)
EMPTY FLAG (EF)
RETRANSMIT (RT)
EXPANSION IN (XI)
(HF)
FIFO
A or B
IDT
7280
7281
7282
7283
7284
7285
(HALF-FULL FLAG)
3208 drw 14
XIA XIB
9
9
18
9
18
HFB
HFA
9
DATA
WRITE (W)
FULL FLAG (FFA)
RESET (RS)
(D)
IN
READ (R)
EMPTY FLAG (EFB)
RETRANSMIT (RT)
DATA
(Q)
OUT
3208 drw 15
FIFO A FIFO B
7280/7281/7282/
7283/7284/7285
9
COMMERCIAL TEMPERATURE RANGE
IDT7280/7281/7282/7283/7284/7285 5V ASYNCHRONOUS FIFO
DUAL 256 x 9, 512 x 9, 1,024 x 9, 2,048 x 9, 4,096 x 9 and 8,192 x 9
JUNE 29, 2012
Figure 14. Block Diagram of 1,024 x 9, 2,048 x 9, 4,096 x 9, 8,192 x 9, 16,384 x 9, 32,768 x 9 FIFO Memory (Depth Expansion)
TABLE 1 — RESET AND RETRANSMIT
Single Device Configuration/Width Expansion Mode
Inputs Internal Status Outputs
Mode RS RT XI Read Pointer Write Pointer EF FF HF
Reset 0 X 0 Location Zero Location Zero 0 1 1
Retransmit 1 0 0 Location Zero Unchanged X X X
Read/Write 1 1 0 Increment
(1)
Increment
(1)
XXX
NOTE:
1. Pointer will increment if flag is High.
TABLE 2 — RESET AND FIRST LOAD TRUTH TABLE
Depth Expansion/Compound Expansion Mode
Inputs Internal Status Outputs
Mode RS FL X I Read Pointer Write Pointer EF FF
Reset First Device 0 0 (1) Location Zero Location Zero 0 1
Reset All Other Devices 0 1 (1) Location Zero Location Zero 0 1
Read/Write 1 X (1) X X X X
NOTE: 10
1. XI is connected to XO of previous device. See Figure 14. RS = Reset Input, FL/RT = First Load/Retransmit, EF = Empty Flag Output, FF = Full Flag Output,
XI = Expansion Input, HF = Half-Full Flag Output
D
W
FFB
EFB
FLB
XOB
RSA
FULL EMPTY
V
CC
R
9
9
99
XIB
9
Q
FFA
EFA
FLA
XOA
XIA
FFB
EFB
FLB
XIB
3208 drw 16
XOA
FIFO A
FIFO B
FIFO A
FIFO B
XIA
XOB
EFA
FLA
FFA
7280/7281/
7282/7283/
7284/7285
7280/7281/
7282/7283/
7284/7285

7285L15PAGI

Mfr. #:
Manufacturer:
IDT
Description:
FIFO FIFO
Lifecycle:
New from this manufacturer.
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