User's Manual

MOL81 485 1312/MOL81 485 1337
MOL81 485 1312-MOL81 485 1337-UM-1.4-EN 11/20
The maximum time allowable between the reception of two characters is a protocol parameter which allows a
slave to resynchronise to a frame-start, if transmission is interrupted. If this time is exceeded, the slave rejects
the frame currently being received.
For the MOL81 MODBUS this time is 2ms.
A general description for the two implemented MODBUS functions is given here. See the following chapters for
a more detailed description of each command.
Write n words (function code 16)
- Command
2 bytes 2 bytes 1 byte n bytes 2 bytes
Device address 10H command nb of words nb of characters values * CRC 16
* words to be written, in order
A word consists of two bytes, high-order byte first
- Reply
2 bytes 2 bytes 2 bytes
Device address 10H command nb of words CRC 16
If the address is 00H, all the devices process the command without sending a reply.
Read n words (function code 3 or 4)
- Command
2 bytes 2 bytes
Device address 03 command nb of words CRC 16
- Reply
1 byte n bytes
Device address 03 nb of characters read
†
values* CRC 16
* bytes read, in order
†
number of characters read = 2 X number of words in Command (always even)
6.2 MODBUS Commands
These commands either perform an action (WRITE) or retrieve information (READ).
The following table contains all commands that can be sent to the device:
N° Commands Fct code Command
(hex)
Data sent Data received
1 Read status 3 or 4 0040
1 word status
nb words = 1
2 Read tag 3 or 4 0042 3 words nb words = 3
3 Emission 125KHz 16 0043
1 word emission
4 Reset device 16 0045 1 byte ( 0 = reset )
5 Read firmware version 3 or 4 0049
1 word version
nb words = 1
6 Write Setup 16 004B
1 word config
7 Write Outputs 16 0052
1 word sortie
6.3 Command: Read last tag code
This command will retrieve the most recently read tag. The reply contains 3 words.