Test-Ok eC-test-mate, Hardware Reference Manual

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STX mode explained
Sending packets in STX mode is a way synchronize the receiver with the stream of bytes that is received.
The principle (and implementation) is simple: each packet starts with a 'Start of Transmission' (STX) byte
which has a unique value that will never be transmitted in the actual packet data. The end of a packet is
marked with another unique value: the 'End of Transmission' byte (ETX). Synchronizing is now very easy for
the receiver: as soon as an STX byte is received, the start of the packet is found and as soon as ETX is
received, the packet has been completely received. Besides the synchronization, another advantage is that
the receiving software does not need to have any knowledge about the packet size.
If the packet contains bytes with the same value as STX and ETX, then these values cannot be transmitted
as such since this would make the receiver resynchronize on the start of a new packet or on the premature
end of the current packet. Instead, a third unique value is defined to 'escape' the normal meaning of the
special values. The DLE (Data Link Escape) byte is therefore inserted into the transmission on every
occurrence of STX, ETX and DLE in the packet data. Thus, when receiving DLE, then this byte shall not be
added to the packet but the next received byte shall be added without interpreting the received value as STX,
ETX or DLE.
Values used by the eC-test-mate Type I:
STX = 0x0F (15
10
)
ETX = 0x04 (4
10
)
DLE = 0x05 (5
10
)
Associated test command(s):
• CONFIG_SERIAL
• TRANSMIT_SERIAL
• SET_SERIAL
• TEST_SERIAL
• WAITTX
• WAITRX