I expect to see broadcast data from a 1553 broadcast command in my RT(non-31) data buffer, but I don’t. How does Alta handle a 1553 broadcast (RT31) message?

If the Alta device is in “multiple RT” mode (which is the default) then it can simultaneously operate as any or all RT addresses.

If the firmware had to copy the broadcast data to 31 RT buffers it could cause timing problems for the next message.  Therefore a “multiple RT” 1553 device stores Broadcast (RT31) data in data buffers for RT31.

For instance, suppose you will expect a boradcast command (RT31) for SA 21. If you currently have RT1 setup with a receive SA 21 buffer, this buffer only gets the messages for RT1 (not RT31 broadcast data).

To receive the broadcast data for this message, simply add RT31 and allocate a receive SA 21 buffer – this is where the Broadcast message data will be stored.  When you read the buffer for broadcast data specify RT address 31 rather than RT1.

You could also set the RT configuration to “single RT” mode (ADT_L1_1553_SetConfig) and set it up as RT1.  In single RT mode the firmware only has to process 1 RT and will put the Broadcast data in the RT 1 receive SA21 buffer.