5

®

ISO508

DATA CORRUPTION

In either synchronous or asynchronous mode if the data is

upset by a transient the complete transmission is invalid.

However, in asynchronous mode the data is being sent

continuously and will therefore correct the corrupted infor-

mation within a maximum of 1

µs. In synchronous mode,

data transfer is under the control of the user, and retransmis-

sion would be required by the software.

DATA TRANSMISSION AND JITTER

Because the internal 20MHz clock is free-running, two

“jitter” conditions are possible. In synchronous mode when

LEI goes low data will be transmitted (clocked) across the

barrier. Depending on when LEI goes low, in relation to the

internal clock cycle, will determine the “jitter” between

successive input data transfers. This can be maximum of

50ns.

In asynchronous mode the input data is transferred by the

internal clock and logic control, i.e., 2 sync. Clock cycles.,

input data is presented, in relation to the start of the data

block transmission, will determine the “jitter” between suc-

cessive input data transfers. This can be maximum of 500ns.

FIGURE 4. Data Corruption.

FIGURE 5. Jitter in Synchronous Mode.

FIGURE 6. Jitter in Asynchronous Mode.

FIGURE 7. Timing Diagrams.

INPUT DATA

LEI

INT. CLK

“JITTER”

INPUT

DATA

LEI

INT. CLK

“JITTER”

210

765

4321

LEO

DATA OUT

OE

t

DD

t

EN

t

DIS

t

WH

LEI

DATA IN

DATA OUT

t

H

t

WL

t

PD(sync)

DATA IN

DATA OUT

t

PD(sync)

t

SU

n–1

INPUT DATA

LEI

BARRIER

LEO

DATA n+1

DATA n+2

DATA n

OUTPUT DATA

DATA n–1

Invalid

DATA n+1

ACTIVE

ACTIVE

ACTIVE