TDA7476 Datasheet, PDF (11/15 Pages) STMicroelectronics – CAR RADIO DIAGNOSTIC PROCESSOR

TDA7476
READ BYTE 1
MSB
LSB
D7
D6
D5
D4
D3
D2
D1
D0
STATUS
0
0
X
X
1
1
X
0 CH1 short circuit to Vs
0
0
X
X
1
1
0
X CH1 short circuit to GND
0
0
X
X
1
1
1
1
0
0
X
X
1
1
1
1
0
0
X
0
1
1
X
X CH2 short circuit to Vs
0
0
0
X
1
1
X
X CH2 short circuit to GND
0
0
1
1
1
1
X
X
0
0
1
1
1
1
X
X
READ BYTE 2
1
1
X
X
1
1
X
0 CH3 short circuit to Vs
1
1
X
X
1
1
0
X CH3 short circuit to GND
1
1
X
X
1
1
1
1
1
1
X
X
1
1
1
1
1
1
X
0
1
1
X
X CH4 short circuit to Vs
1
1
0
X
1
1
X
X CH4 short circuit to GND
1
1
1
1
1
1
X
X
1
1
1
1
1
1
X
X
READ BYTE 3
1
1
X
X
X
X
1
0 AUX1 short circuit to GND
1
1
X
X
X
X
0
1 AUX1 open load
1
1
X
X
1
0
X
X AUX2 short circuit to GND
1
1
X
X
0
1
X
X AUX2 open load
1
1
X
0
X
X
X
X CH5 short circuit to Vs
1
1
0
X
X
X
X
X CH5 short circuit to GND
1
1
1
1
X
X
X
X
1
1
1
1
X
X
X
X
Repetitive turn-on diagnostic
During the turn-on diagnostic, the TDA7476 can reveal false ”short circuit across load” and/or false ”open
load” due to noise sources such as door slams.
This problem can be solved doing more than one turn-on diagnostic routine. If the µP asks for N times
the state of the audio system, it has to consider a fault as really present only if it is detected in all the N
turn-on diagnostic.
As above explained, the first time the TDA7476 receivers the byte ADD1, it does the turn-on diagnostic;
then each timeit is addessed with ADD1, it does the permanent diagnostic. This is not true if, when the
µP sends for the forst time the byte ADD2, it does not send to the TDA7476 the acknowledge after it has
received the byte BYTE3. In this case, the TDA7476 does not switch from turn-on to permanent diagnos-
tic mode so if it receives again the byte ADD1 it works as it was the first time that it does the turn-on di-
agnostic. In order to do repetitive turn-on diagnostic, the µP has to be programmed as following:
Step 1: the µP sends ADD1
START
ADD1
ACK
STOP
Step 2: the µP waits Twait1 seconds
Step 3: the µP sends ADD2, receives BYTE1, BYTE2, BYTE3, does not send the acknowlegde af-
ter BYTE3
START
ADD2
ACK
BYTE1
ACK
BYTE2
ACK
BYTE3
STOP
Step 4: repeat Step1, Step2, Step3 while the second, third, fourth, ...turn-on diagnostic has to be
done.
During the last turn-on diagnostic the µP sends ADD2, receives BYTE1, BYTE2, BYTE3, and
sends the acknowlegde after BYTE3
START ADD2
ACK
BYTE1
ACK
BYTE2
ACK
BYTE3
ACK
STOP
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