Datasheet

SN74ALVC7804
512 × 18
FIRST-IN, FIRST-OUT MEMORY
SCAS432 – JANUARY 1995
5
POST OFFICE BOX 655303 DALLAS, TEXAS 75265
DATA WORD NUMBERS FOR FLAG TRANSITIONS
DEVICE
TRANSITION WORD
DEVICE
A B C D E F G H I
SN74ALVC7804 W256 W(512Y) W512 W257 W258 W(512X) W(513X) W511 W512
offset values for AF/AE
The AF/AE flag has two programmable limits: the almost-empty offset value (X) and the almost-full offset value
(Y). They can be programmed after the FIFO is reset and before the first word is written to memory. The AF/AE
flag is high when the FIFO contains X or less words or (512 minus Y) or more words.
To program the offset values, PEN
can be brought low after reset. On the following low-to-high transition of
LDCK, the binary value on D0D7 is stored as the almost empty offset value (X) and the almost full offset value
(Y). Holding PEN
low for another low-to-high transition of LDCK reprograms Y to the binary value on D0D7
at the time of the second LDCK low-to-high transition. Writes to the FIFO memory are disabled while the offsets
are programmed. A maximum value of 255 can be programmed for either X or Y (see Figure 2). To use the
default values of X = Y = 64, PEN
must be held high.Figure 1
LDCK
RESET
X and Y Y
PEN
D0D17
EMPTY
Don’t Care
Don’t Care
Figure 2. Programming X and Y Separately