LOADING DATA

Data can be entered whenever the DATA-IN READY

(DIR) flag is high, by a low to high transition on the

SHIFT-IN (SI) input. This input must go low momen-

tarily before the next word is accepted by the FIFO.

The DIR flag will go low momentarily, until the data

have been transferred tothe second location. The flag

will remain low when all 16-word locations are filled

with valid data, and further pulses on the SI input will

be ignored until DIR goes high.

UNLOADING DATA

As soon as the first word has rippled to the output,

DATA-OUT READY (DOR) goes high, and data can

be removed by afalling edge on theSO input. This fall-

ing edge causes the DOR signal to go low while the

word on the output is dumped and the next word

moves to the output. As long as valid data are avail-

able in the FIFO, the DOR signal will go high again sig-

nifying that the next word is ready at the output. When

the FIFO is empty, DOR will remain low, and any fur-

ther commands will be ignored until a ”1” marker

ripples down to the last control register, when DOR

goes high. Unloading of data is inhibited while the 3-

state control input is high. The 3-state control signal

should not be shifted from high to low (data outputs

turned on)while the SHIFT-OUT is at logic 0. This level

change would cause the first word to be shifted out

(unloaded) immediately and the data to be lost.

CASCADING

The HCC/HCF40105B can be cascaded to form

longer registers simply by connecting the DIR to SO

and DOR to SI. In the cascaded mode, a MASTER

RESET pulse must be applied after the supply voltage

is turned on. For words wider than 4 bits, the DIR and

the DOR outputs must be gated together with AND

gates. Their outputs drive the SI and SO inputs in par-

allel, if expanding is done in both directions.

3-STATE OUTPUTS

In order to facilitate data busing, 3-state outputs are

provided on the data output lines, while the load con-

dition of the register can be detected by the state of

the DOR output.

MASTER RESET

A high on the MASTER RESET (MR) sets all the con-

trol logic marker bits to ”0”. DOR goes low and DIR

goes high. The contents of the data register are not

changed, only declared invalid, and will be super-

seded when the first word is loaded.

APPLICATIONS INFORMATION

EXPANSION, 8 BITS–WIDE–BY–16 N–BITS LONG.

HCC/HCF40105B

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