USR-N668 User Manual Technical Support:
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47
Figure 68 AT command
Figure 69 Time sequence diagram
Time requirements:
T1 > serial port packing interval
T2 < < 300ms
T3 < < 300ms
T5 < < 3S
The transition from transmissions mode to temporary instruction mode:
1. The serial port device sends "++" to the module continuously. When the module receives "++", it sends a "a" to the
device. No data can be sent before sending "+ + +".
2. When the device receives "a", it must send a "a" to the module within 3 seconds.
3. After receiving the "a", module sends the "+OK" to the device and enters the "AT instruction mode".
4. When the device receives "+OK", it knows that the module has entered "AT instruction mode" and can send AT
instructions to it.
Switching from the AT instruction mode to the network pass through sequence:
1. The serial port sends the instruction "AT+ENTM" to the module.
2. Module returns the "+OK" after receiving the instruction and returns to the previous mode.
5.3.2.
Error code
Table 10 Error code
Error code
Describe
-1
Invalid command format
-2
Invalid command
-3
Invalid operator
-4
Invalid parameters
-5
operation not permitted
