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Entering the Serial Programming Mode
Before issuing commands, the DS must listen (i.e, be in programming mode). There are two ways to enter Serial Programming mode, and they are both described under Serial Parameters (Modem Commands) in AN008. Using HyperTerminal.
Once you enter Serial Programming mode, you can start issuing commands. Basic command format is described under Sending a Command (Command Format).
One of the most important things to remember about commands is that they are asynchronous. In simple terms, this means that when you issue a command and get back an A (Ack) response, the command has not necessarily been executed. The A means that the DS has received your command and has started executing it.
This is most prominent when issuing instructions to establish or close connections. When sending such instructions, the A reply comes immediately -- the DS takes very little time to receive and 'understand' the instruction. But having understood it, it now has to execute it -- and that sometimes takes time.
The time it takes to establish a TCP connection varies according to the topology of the network the DS is in. Thus, after issuing an instruction such as the Establish Connection (CE) instruction, you must check the DS status to see when the connection has actually been established. For this, use the Echo (X) command. This is described in detail under Finding Out Connection Status (X).