IDT7203/7204/7205/7206 CMOS ASYNCHRONOUS FIFO
2048 x 9, 4096 x 9, 8192 x 9 and 16384 x 9
MILITARY AND COMMERCIAL TEMPERATURE RANGES
Figure 11. Expansion In
2661 drw 11
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). For additional information, refer to Tech Note 8: Oper-
ating FIFOs on Full and Empty Boundary Conditions and
Tech Note 6: Designing with FIFOs.
Single Device Mode
A single IDT7203/7204/7205/7206 may be used when the
application requirements are for 2048/4096/8192/16384 words
or less. The IDT7203/7204/7205/7206 is in a Single Device
Configuration when the Expansion In (XI) control input is
grounded (see Figure 12).
The IDT7203/7204/7205/7206 can easily be adapted to
applications when the requirements are for greater than 2048/
4096/8192/16384 words. Figure 14 demonstrates Depth Ex-
pansion using three IDT7203/7204/7205/7206s. Any depth
can be attained by adding additional IDT7203/7204/7205/
7206s. The IDT7203/7204/7205/7206 operates in the Depth
Expansion mode when the following conditions are met:
1. The first device must be designated by grounding the First
Load (FL) control input.
2. All other devices 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.
For additional information, refer to Tech Note 9: Cascading
FIFOs or FIFO Modules.
Word width may be increased simply by connecting the
corresponding input control signals of multiple devices. Sta-
tus flags (EF, FF and HF) can be detected from any one device.
Figure 13 demonstrates an 18-bit word width by using two
IDT7203/7204/7205/7206s. Any word width can be attained
by adding additional IDT7203/7204/7205/7206s (Figure 13).
Applications which require data buffering between two
systems (each system capable of Read and Write operations)
can be achieved by pairing IDT7203/7204/7205/7206s as
shown in Figure 16. Both Depth Expansion and Width Expan-
sion may be used in this mode.
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 (tWEF + 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.
The two expansion techniques described above can be
applied together in a straightforward manner to achieve large
FIFO arrays (see Figure 15).