EK-TM4C1294XL: 9 bit UART address mask

Norbert Toth

Part Number: EK-TM4C1294XL

Hi Folks,

I wanted to build a distributed network based on RS485 bus communication with 9 bit UART configuration. I have 1 dedicated master, and 5 slave nodes in range of addresses between 1 to 5. To do this, I have implemented a modbus stack, where all of the slaves are waiting for the "9_bit_interrupt" and its subsequent bytes.

As I understood from the data sheet, if I set the address mask to 0xFF, the UART listen only its address. This works fine.

Then I tried to set an address mask to the first complement of the address, that caused that every slaves got every messages on the bus, which is not what I wanted.

Can anybody explain me, how can I use this address mask, how can I configure address ranges, etc?

Regards,

Norbert

over 7 years ago

0 Charles Tsai over 7 years ago

TI__Guru**** 191466 points

Hi Nobert,
Let me give an example. Let's say you want a UART slave to identify with an address equal to 0xAA then you would set the address register to 0xAA and the mask to 0xFF. I think you go this working. If you want the slave to identify as either 0xAA or 0xAB then you will set the address register to 0xAA and set the mask to 0xFE. If you set the mask to 0xFC then the slave is identified with address equal to 0xA8, 0xA9, 0xAA and 0xAB.

0 Norbert Toth over 7 years ago in reply to Charles Tsai

Expert 1145 points

Hi Charles,

so can we say, where the bit mask contains "1", the periphery expects exact match, but in positions filled by "0", matching is not expected?

Regards,
Norbert

0 Charles Tsai over 7 years ago in reply to Norbert Toth

TI__Guru**** 191466 points

Yes, that is correct.

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EK-TM4C1294XL: 9 bit UART address mask