9
Serial port (RS485)
Communication protocol for connecting with an external device.
Sending
The Indutel GSM sends
STX (start of text, 02 hex)
The Indutel GSM waits for
DLE (data link escape, 10 hex) If a NAK (negative acknowledgement) or any other signal
is sent back as a DLE or there is a timeout, sending is
repeated 3 times. Sending is terminated after three
unsuccessful attempts.
After receiving the DLE, Indutel GSM transmits a data byte
Value and meaning of the data byte:
DLE
ETX (end of text, 03 hex)
and waits for
81 hex
82 hex
83 hex
84 hex
Ringing has started
Ringing has stopped
Receiver was lifted
Recover was replaced
Receiving
DLE
If a NAK (negative acknowledgement) or any other signal is
sent back as a DLE or there is a timeout, sending is repeated
6 times. Sending is terminated after 6 unsuccessful
attempts.
The external apparatus sends
STX
and waits for
DLE
which is sent by Indutel GSM when it is ready to receive data.
After receiving the DLE, the external apparatus sends
1. Data byte
2. Data byte
DLE
ETX
value and meaning of the data byte C1 or C2
8 bit value
If transmission has been successful, Indutel GSM sends
DLE
If the data received is not correct or reception was impaired, Indutel GSM sends
NAK
requesting a repeat of the transmission. This request will be repeated 6 times. After 6 failed
attempts, sending will be terminated.
Receiving data should trigger an SMS which states:
Alarm1 (2), 2. Data byte.
