Because no built-in mechanism verifies the validity of the data exchanged through the UART, a custom implementation was developed for this design. The message sent through the UART must always have 23 long formatted characters, as follows:
| Characters Position | Name | Description |
|---|---|---|
| 0 - 3 | Header | Indicates if the message originates from the MicroBlaze V (m2c{) or the web console (c2m{). |
| 4 - 19 | Payload | Contains the information shared between the MicroBlaze V and the web console. |
| 20 - 22 | Tail | Closes the payload (}) and the last two characters correspond to the checksum to validate the payload. |
The header can only have two valid values. If the message originates from the MicroBlaze V processor and is designated for the web console, it uses the value “m2c”. If it originates from the other direction, it uses the value “c2m”. The fourth character is an opening curly brace ({), indicating that the next characters are the payload. If any characters are lost, then the header also resyncs with the web console and the MicroBlaze V processor.
The payload always consists of 16 characters long and contains the information shared between the MicroBlaze V and the web console. It contains an update to apply to one of the output devices or an update of the value from one of the input devices.
The tail starts with a closing curly brace (}), indicating the end of the payload. The last two characters represent the checksum results calculated using the CRC16 CCIT algorithm.