SN74ACT7802

1024

× 18 STROBED FIRST-IN, FIRST-OUT MEMORY

SCAS187D – AUGUST 1990 – REVISED APRIL 1998

5

POST OFFICE BOX 655303

offset value values for AF/AE

The FIFO memory status is monitored by the FULL, EMPTY, HF, and AF/AE flags. The FULL output is low when

the memory is full; the EMPTY output is low when the memory is empty. The HF output is high when the memory

contains 512 or more words and low when it contains fewer than 512 words. The level of the AF/AE flag is

determined by both the number of words in the FIFO and a user-definable offset X. AF/AE is high when the FIFO

is almost full or almost empty, i.e., when it contains X or fewer words or (1024 – X) or more words. The AF/AE

offset value is either user-defined or the default value of 256; it is programmed during each reset cycle as follows:

user-defined X:

Take DAF from high to low.

If RESET is not already low, take RESET low.

With DAF held low, take RESET high. This defines the AF/AE flag using X.

default X:

To redefine the AF/AE flag using the default value of X = 256, hold DAF high during the reset cycle.