Synchronization Word Detection（0Xb5; Send Head Information (0X01/0X81) - SimTech SimCom SIM800 Series Application Note

Smart Machine Smart Decision
1.2 Synchronization Word Detection（0xB5）
When the module Bootloader program starts, if it receives the 0xb5 byte synchronization word
within 100 ms, it will reply with a 0x5b byte word then the module go into the upgrade mode.
Within 100 ms, if the module does not receive 0xb5 synchronization word, the module will enter
normal mode.
Note: in order to ensure the module receive synchronization byte 0xb5, send the bytes within 100
ms after power on.
Figure 2：Waiting for synchronization word
Figure 3：Synchronization word detection

1.3 Send Head Information (0x01/0x81)

Command word 0x01 means there is no need to erase the file system of the module, while 0x81
means it needs to erase the file system of the module, Data head contains 128-byte information
that included in the front part of upgrade file.
SIM800 Series_Software Upgrade_Application Note_V1.02 2014-06-30
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