Pin Names

Description

CP

Clock Pulse Input

DS

0

Serial Data Input for Right Shift

DS

7

Serial Data Input for Left Shift

S

Mode Select Inputs

MR

Asynchronous Master Reset

OE

TRI-STATE Output Enable Inputs

I/O

Parallel Data Inputs or

TRI-STATE Parallel Outputs

Q

Serial Outputs

Functional Description

The ’AC/’ACT299 contains eight edge-triggered D-type

flip-flops and the interstage logic necessary to perform syn-

chronous shift left, shift right, parallel load and hold opera-

tions. The type of operation is determined by S

shown in the Truth Table. All flip-flop outputs are brought out

through TRI-STATE buffers to separate I/O pins that also

serve as data inputs in the parallel load mode. Q

also brought out on other pins for expansion in serial shifting

of longer words.

A LOW signal on MR overrides the Select and CP inputs and

resets the flip-flops. All other state changes are initiated by

the rising edge of the clock. Inputs can change when the

clock is in either state provided only that the recommended

setup and hold times, relative to the rising edge of CP, are

observed.

A HIGH signal on either OE

buffers and puts the I/O pins in the high impedance state. In

this condition the shift, hold, load and reset operations can

still occur. The TRI-STATE buffers are also disabled by HIGH

signals on both S

operation.

Truth Table

Inputs

Response

MR

S

1

S

0

CP

L

X

X

X

Asynchronous Reset;

Q

HHH

N

Parallel Load; I/O

HLH

N

Shift Right; DS

Q

HH

L

N

Shift Left, DS

Q

H

L

L

X

Hold

H = HIGH Voltage Level

L = LOW Voltage Level

X = Immaterial

www.national.com

2