SN74ACT7200L, SN74ACT7201LA, SN74ACT7202LA

256

× 9, 512 × 9, 1024 × 9

ASYNCHRONOUS FIRST-IN, FIRST-OUT MEMORIES

SCAS221A – FEBRUARY 1993 – REVISED SEPTEMBER 1995

17

POST OFFICE BOX 655303

APPLICATION INFORMATION

Combining two or more devices to create one FIFO with a greater number of memory bits is accomplished in two

different ways. Width expansion increases the number of bits in each word by connecting FIFOs with the same depth

in parallel. Depth expansion uses the built-in expansion logic to daisy-chain two or more devices for applications

requiring more than 256, 512, or 1024 words of storage. Width expansion and depth expansion can be used together.

width expansion

Word-width expansion is achieved by connecting the corresponding input control to multiple devices with the

same depth. Status flags (EF, FF, and HF) can be monitored from any one device. Figure 14 shows two FIFOs

in a width-expansion configuration. Both devices have their expansion-in (XI) inputs tied to ground. This

disables the depth-expansion function of the device, allowing the first-load/retransmit (FL/RT) input to function

as a retransmit (RT) input and the expansion-out/half-full (XO/HF) output to function as a half-full (HF) flag.

depth expansion

The SN74ACT7200L / 7201LA / 7202LA is easily expanded in depth. Figure 15 shows the connections used to

depth expand three SN74ACT7200L / 7201LA / 7202LA devices. Any depth can be attained by adding additional

devices to the chain. The SN74ACT7200L / 7201LA / 7202LA operates in depth expansion under the following

conditions:

all EF outputs must be ORed together.

combined depth and width expansion

Both expansion techniques can be used together to increase depth and width. This is done by first creating

depth-expanded units and then connecting them in a width-expanded configuration (see Figure 16).