Flyron FN-BC20 - 4 Serial Control Mode; Command Format; About Checksum

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Flyron Technology Co., Ltd. 20 Channel MP3 Sound Board
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4. Serial Control Mode
Supports RS232 and RS485 serial control modes. Both of these two control modes share the same
communication protocols as below. Regarding RS485, we employed half-duplex communication standard.
4.1. Command Format
 Communication baud rate: 9600 bps
 Data bits: 1
 Checkout: none
 Flow Control: none
Format: $S / Ver. / Number / Command / Feedback / Param_MSB / Param_LSB / Check_MSB / Check_LSB / $O
$S
Start byte 0x7E
Ver.
Version byte, 0xFF by default
Number
Number of bytes from version info to Check_LSB, typically 0x06 (checks um not counted)
Command
Command byte
Feedback
0x01: Need feedback --send confirmation back to MCU; 0x00: No need feedback
Param_MSB
Most significant byte of parameter
Param_LSB
Least significant byte of parameter
Check_MSB
Most significant byte of checksum
Check_LSB
Least significant byte of checksum
$O
End byte 0xEF
For example, if we specify playback of SD card, we need to send the command “7E FF 06 09 00 00 02 FF F0 EF”. The number
is 6 bytes, and these 6 bytes are “FF 06 09 00 00 02”. Start byte, end byte and checksum are not counted.
4.2. About Checksum
Regarding to calculating checksum, set your 16 bit checks um value to 0. For each byte from the Version byte until the
Param_LSB byte, subtract the byte from the checksum.
Normally it‟s okay whether users choose to use checksum or not, our module can receive serial data with or without checksum,
but some of users may use a MCU without crystal oscillator, so if so we strongly suggest users to add checksum to make sure
the communication stability.