UART Transmitter Sends Bytes Out of Order

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In the first piece of code (the not working one) in SEND_BYTES state you wrote:

tbyte = plain_text[byteN*8 +: 8];

What does that mean?

I have never seen such a syntax. Is this a typo?

I'd rather used:

tbyte = plain_text[(byteN+1)*8: byteN*8];

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Check section 4.2.1 of the 1364-2001 spec, Vector bit-select and part-select addressing

fe, if you declare a reg as:

reg [15:0] d,

then d[0 +: 8] is equivalent to d[7:0]

if you declare it as:

reg [0:15] d,

then d[0 +: 8] is equivalent to d[0:7]

there is also a -: operator that works similarly

As for the question in hand, you should get a simulator (there are free ones), and check your timing constraints