Posted on Feb 6, 2014

Every IC on the I ²C bus requires a unique address. Usually such ICs can select from a set of 2 to 8 possible addresses to allow multiple chips of the same type on one bus. The SAA1064 can select from 4 different addresses by applying a specific voltage on pin 1 (ADR). Unfortunately the address pin on my module is hard wired to ground.

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Therefore changing the address of it requires some cutting and rewiring. Fortunately that is only required when more than one module is to be used on the same I ²C bus. The track just above C02 (the small brown part in the upper right hand corner) is the track that connects the ADR pin of the SAA1064 to ground (right side of C02). By cutting this track and connecting pin 1 of the SAA1064 directly to the Vcc you can simply select address $76 instead of $70. Selecting any of the other address involves adding 2 resistors to create the appropriate voltage on pin 1. A voltage of about 1. 9V will select addres $72, while a voltage about 3. 1V will select address $74. The diagram above shows a complete I ²C message. Such a message consists of an address byte and a total of 6 data bytes. The diagram only shows a write message. You can read from the device, but that will only tell you whether it was just powered up. Thus not very useful, so I will restrict myself to the write mode only. The address byte is mainly fixed, only 2 bits may differ depending on the voltage on the ADR pin. On my module the ADR pin is hard wired to ground, which makes it respond to address $70. The first data byte in the string is always a sub-address. It selects what data byte is to be send next. In most cases this sub-address byte is $00, which means that the next data byte is the control byte. By using other sub-addresses you can skip right to the data...

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