Functional description

L9822E

12/17

4.6

Fault conditions check

Checking for fault conditions may be done in the following way. Clock in a new control byte.

Wait 160 µs or so to allow the outputs to settle.

Clock in the same control byte and observe the diagnostic data that comes out of the device.

The diagnostic bits should be identical to the bits that were first clocked in. Any differences

would point to a fault on that output. If the output was programmed ON by clocking in a zero,

and a one came back as the diagnostic bit for that output, the output pin was still high and a

short circuit or overload condition exists.

If the output was programmed OFF by clocking in a one, and a zero came back as the

diagnostic bit for that output, nothing had pulled the output pin high and it must be floating,

so an open circuit condition exists for that output.

Figure 4.

Byte timing with asynchronous reset.

Figure 5.

Timing diagram.

RESET

CE

SCLK

SI

#7

#6

#5

#4

#3

#2

#1

#7

#6

#5

#4

#3

#2

#1

#0

NEW

RESET

FAULTS

SO

OUTPUTS

OLD

CE

SCLK

SI

SO

OUTS

OLD

NEW

TUD

TDIS

DI0

TLAG

DI7

TH

#6

#7

I/FOP

TWSCKH

TLEAD

#0

TWSCKL

TSU

TV

TEN

THD

D00

D06

D07

TPHL

TPLH

FAULT-INDUCED

TURN/OFF