AS1123
Datasheet ꢀ Detailed Description
Detailed Shorted-LED Error Report
The detailed shortedꢀLED error report can be read out immediately after global error mode has been run (see Global Error Mode on page 10).
SDI must be 1 for the first device.
Figure 16. Detailed Shorted-LED Error Report Timing Diagram
Global Flag Readout
Detailed Error Report Readout
OEN
LD
tTESTING
tSU(ERROR)
tH(L)
tP4
tGSW(ERROR)
tGSW(ERROR)
CLK
tGSW(ERROR)
Don’t
Care
DBit15
DBit14 DBit13 DBit12 DBitn DBit2 DBit1 DBit0
SDI
tSW(ERROR)
SFLAG
New Data Input
Don’t
Care
SBit15 SBit14 SBit13 SBit12 SBitn SBit2 SBit1 SBit0
O
FLAG
T
FLAG
TFLAG
SDO
Shorted-LED Error Report Output
tP4
tP1
For detailed timing information see Timing Diagrams on page 8.
Detailed ShortedꢀLED Error Report Example
Consider a case where three AS1123s are cascaded in one chain. A 1 indicates a LED is on, a 0 indicates a LED is off, and an X indicates a
shorted LED. This test is used onꢀtheꢀfly.
IC1:[11111XX111111111] IC2:[1111111111111111] IC3:[X100011111111111]
IC1 has two shorted LEDs which are switched on, IC3 has one shorted LED switched off due to input. 3*16 clock cycles are needed to write the
entire error code out. The detailed error report would look like this:
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 0 0 0 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 X X 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 X 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
Input Data:
LED Status:
Failure Code:
Showing IC1 as the device with two shorted LEDs at position 6 and 7, and IC3 with one shorted LED at position 1. The shorted LED at position 1
of IC3 cannot be detected, since LEDs turned off at test time are not tested and will show a logic "1" at the detailed error report. To test all LEDs
this test should be run with an all 1s test pattern. For a test with an all on test pattern, lowꢀcurrent diagnostic mode should be entered first to
reduce onꢀscreen flickering.
Note: In an actual report there are no spaces in the output. LEDs turned off during test time cannot be tested and will show a logic 1 in the
detailed error report.
Low-Current Diagnostic Mode
To run the openꢀ or shortedꢀLED test, a test pattern must be used that will turn on each LED to be tested. This test pattern will cause a short
flicker on the screen while the test is being performed. The lowꢀcurrent diagnostic mode can be initiated prior to running a detailed error report to
reduce this onꢀscreen flickering.
Note: Normally, displays using such a diagnostic mode require additional cables, resistors, and other components to reduce the current. The
AS1123 has this currentꢀreduction capability builtꢀin, thereby minimizing the number of external components required.
Lowꢀcurrent diagnostic mode can be initiated via 3 clock pulses during errorꢀdetection mode. After the falling edge of LD, a test pattern displaying
all 1s can be written to the shift register which will be used for the next errorꢀdetection test.
On the next falling edge of OEN, current is reduced to ILC. With the next rising edge of OEN the current will immediately increase to normal levꢀ
els and the detailed error report can be read out entering errorꢀdetection mode.
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