Appendix A: Communication A.2 Protocol Description
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Examples of MODBUS Master Requests
Here are some examples of read/write operations in a MODBUS Master system.
The syntax is an example and differs between different master systems.
Comli Communication
Comli is a general asynchronous, serial communication protocol, utilizing the
master/slave relationship and communication in only one direction at the time
(Half-duplex).
ECA can only work as a Comli slave and supports the following message types.
Type 0 – transfer of I/O RAM Status or Register value.
Type 1 – acknowledge correctly received data.
Type 2 – request of I/O RAM Status or Register value
Type 3 – transfer of status for one I/O bit.
Type 4 – request of status for one I/O bit.
Message Structure
There are five message types recognised by the controller. Each message type sent
has a given number of characters, or more precisely, a given number of bytes of
02 Illegal data address
03 Illegal data value
Operation Syntax in Master Operation in ECA
Read Coil Status C3 Read I/O RAM Map bit 3
Read Input Status I1076 or I10076 Read I/O RAM Map bit 76
Read Holding Registers HR4006, HR40006 Read Register Map R6 (AIC6)
Read Input Registers IR3033, IR30033 Read Register Map R33 (AI1)
Force Single Coil C208 Write I/O RAM Map bit 208
Preset Single Register IR3052, HR4052,
IR30052, HR40052
Write Register Map R52
(ISP1)
Code Name
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