group of optocouplers which are

operating under the same

conditions (i.e., the same drive

current, supply voltage, output

load, and operating tempera-

ture). As illustrated in Figure

17, if the inputs of a group of

optocouplers are switched either

ON or OFF at the same time,

the shortest propagation delay,

longest propagation delay,

determine the maximum

parallel data transmission rate.

Figure 18 is the timing diagram

of a typical parallel data

application with both the clock

and the data lines being sent

through optocouplers. The

figure shows data and clock

signals at the inputs and

outputs of the optocouplers. To

obtain the maximum data

transmission rate, both edges of

the clock signal are being used

to clock the data; if only one

edge were used, the clock signal

would need to be twice as fast.

Propagation delay skew

represents the uncertainty of

where an edge might be after

being sent through an

optocoupler. Figure 18 shows

that there will be uncertainty in

both the data and the clock

lines. It is important that these

two areas of uncertainty not

overlap, otherwise the clock

signal might arrive before all of

the data outputs have settled, or

some of the data outputs may

start to change before the clock

signal has arrived. From these

considerations, the absolute

minimum pulse width that can

be sent through optocouplers in

a parallel application is twice

use a slightly longer pulse width

to ensure that any additional

uncertainty in the rest of the

circuit does not cause a

problem.

offers the advantages of

guaranteed specifications for

propagation delays, pulse-width

distortion and propagation

delay skew over the

recommended temperature,

input current, and power supply

ranges.

For more information call: United States: call your local HP sales office listed in your telephone directory. Ask for a Components

representative. Canada: (416) 206-4725 Europe: (49) 7031/14-0 Asia Pacific/Australia: (65) 290-6360 Japan: (81 3) 3331-6111

Printed in U.S.A.

Data Subject to Change

Obsoletes 5954-1031 (1/86), 5954-0960 (12/83)

5091-9125E (12/93)

Copyright © 1993 Hewlett-Packard Co.

Figure 17. Illustration of Propagation Delay

Skew - t

Figure 18. Parallel Data Transmission Example.

50%

1.5 V

V

O

50%

1.5 V

DATA

INPUTS

CLOCK

DATA

OUTPUTS

CLOCK

H