SN74ALVC7813

64

× 18

LOW-POWER CLOCKED FIRST-IN, FIRST-OUT MEMORY

SCAS594A – OCTOBER 1997 – REVISED APRIL 1998

8

POST OFFICE BOX 655303

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 = 8 are used. The AF/AE flag is high when the FIFO

contains X or fewer words or (64 – 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 63 can be programmed

for either X or Y (see Figure 4). To use the default values of X = Y = 8, PEN must be held high.

34

RESET

WRTCLK

PEN

WRTEN1

WRTEN2

D0–D7

IR

X and Y

Y

Figure 4. Programming X and Y Separately