Starting up the device - RS 485 Modbus interface
Leuze electronic GmbH + Co. KG
CML 730i
161
14.4.4 Changeover from autosend mode to RS 485 Modbus
To switch back from autosend mode to RS 485 Modbus, the control (RS 485 Modbus master) must send
an “End-Of-Transmission” (EOT) byte (0x04) to the CML 700i.
In the autosend transmission frame, a time window is provided for receiving the EOT byte. The time
window in which the control may send the EOT byte begins after approx. 1.5 characters (start time) after
the CML 700i has received the last character. The character must be transmitted within the time window
of approx. 3 characters. The times are multiples of 100 µs. For high bit rates, the start time is fixed at
100 µs and the entire EOT-byte time window is 200 µs long.
The time window for receiving the EOT byte is only closed when the end of the next measurement cycle
is reached and when the minimum waiting time specified in the table has expired.
5+n+2
Send
16-bit checksum of bytes 1 … 5+n-1 high byte high digit
5+n+3
Send
16-bit checksum of bytes 1 … 5+n-1 high byte low digit
5+n+4
Send
ETX– end detection (0x03)
Changeover
Changeover to receiving;
CML 700i waits for EOT byte (0x04) from the control (Modbus master)
Changeover
Changeover to send if no EOT byte was received
Repeat with byte 0, etc., if autosend is not stopped
Byte no.
Direction of RS 485
(from the perspective of
the CML 700i)
Description
Bit rate
(bit/s)
Pause for EOT byte
(N * 100 µs)
Description
4,800
27
Time window for receiving the EOT byte
9,600
13
19,200
6
38,400
3
57,600
2
115,200
1
921,600
1
