SN74ALVC7804_07 Datasheet, PDF (5/13 Pages) Texas Instruments – 512 × 18 FIRST-IN, FIRST-OUT MEMORY

DEVICE
SN74ALVC7804
A
W256
SN74ALVC7804
512 × 18
FIRST-IN, FIRST-OUT MEMORY
SCAS432 – JANUARY 1995
DATA WORD NUMBERS FOR FLAG TRANSITIONS
TRANSITION WORD
B
C
D
E
F
W(512 – Y) W512
W257
W258 W(512 – X)
G
W(513 – X)
H
W511
I
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 D0 – D7 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 D0 – D7
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
RESET
LDCK
PEN
Don’t Care
D0 – D17
EMPTY
Don’t Care
X and Y
Y
Figure 2. Programming X and Y Separately
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265
5