SN74ALVC7805 Datasheet, PDF (8/14 Pages) Texas Instruments – 256 × 18 LOW-POWER CLOCKED FIRST-IN, FIRST-OUT MEMORY

SN74ALVC7805
256 × 18
LOW-POWER CLOCKED FIRST-IN, FIRST-OUT MEMORY
SCAS593A – OCTOBER 1997 – REVISED APRIL 1998
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. If the
offsets are not programmed, the default values of X = Y = 32 are used. The AF/AE flag is high when the FIFO
contains X or fewer words or (256 – Y) or more words.
Program enable (PEN) should be held high throughout the reset cycle. PEN can be brought low only when IR
is high. On the following low-to-high transition of WRTCLK, 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 WRTCLK reprograms Y to the binary value on D0–D7 at the time of the second WRTCLK
low-to-high transition. When the offsets are being programmed, writes to the FIFO memory are disabled,
regardless of the state of the write enables (WRTEN1, WRTEN2). A maximum value of 127 can be programmed
for either X or Y (see Figure 4). To use the default values of X = Y = 32, PEN must be held high.
RESET
WRTCLK ³
4
PEN
D0–DÎÎ7 ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎXandY
ÎÎÎÎÎÎÎÎÎÎÎÎÎÎ
Y ÎÎÎÎÎÎÎÎÎÎÎÎ
IR
WRTEN^ÎÎ1 ^{ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ}
WRTENÎÎ2 ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ
Figure 4. Programming X and Y Separately
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