OG_MU-4-434_v10e Circuit Design, Inc.
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OPERATION GUIDE
8.5 Data format
8.5.1
Data frame structure
When transmitting and receiving serial data in the transparent mode, configure a data frame with a preamble,
ID code and so on, to ensure that the necessary data is transmitted.
A general data frame consists of Preamble, ID code, User data and Data-check and is transmitted/received as
a packet data. Dummy data is added to the end if necessary.
Preamble
A preamble data is required to match the timing between transmission and reception. At the start of data
transmission, the transmitter transmits data including alternate low and high signals for a certain period of
time. A recommended preamble pattern is 11001100....of more than 20 ms.
ID code
An ID code is a unique code to identify own system from other systems. The receiver determines if the
received data is sent to itself. To avoid erroneous reception, it is recommended to use an ID code with
appropriate length.
User data
A user data is data the user intends to send/receive. To prevent data from being garbled, it is recommended
that the user data has periodical transitions between 1 and 0.
*With the MU-4, ensure that continuous 1 or 0 is limited to 6 ms or less (28 bits for 4800 bps).
Data-check
A data-check (such as CRC) is used to check if the transferred data has errors or not. The receiver
determines if the received data is valid or not.
Dummy data
When transmitting data using UART, there is a time lag from when the last data is set to the transmission
register until UART output is actually completed.
If transmission is turned off or switched before the last bit is output, the last bit may be lost.
Such errors can be avoided by adding dummy data to the end of the data frame.
* You can also avoid the last bit from being lost by controlling the timing of turning off transmission or TX/RX
switching with the MU-4.
Example data format
Preamble
ID code
User data
Data-check
Dummy data
11001100....
CH
01 02 03 04
CC
CC
Repeated 0xCC
> 20 ms
1 byte
ID
4bytes
18 bytes
CRC
2bytes
2 bytes