Modbus Parameter Specifications

Table Of Contents
MODBUS ACE V1.00
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AM ·Page 7 of 78
Form 1003
1 Protocol frame
Data transmission using the MODBUS protocol defined in this specification
takes place solely in an environment defined as Master - Slave system. The ordered flow of data is governed
by the master. A slave has to respond to a command request from the master. When structuring a system, it is
therefore important to ensure that a slave address is not allocated twice.
The preferred transmission medium is a twisted-pair cable with RS485 standard.
RTU is the only transmission mode supported (see MODBUS over Serial Line Specification & Implementation
guide V1.0, Section 2.5.1)
ASCII transmission mode is not supported!
1.1 Byte structure
In accordance with the MODBUS over Serial Line Specification & Implementation guide V1.0, a byte has the
following structure:
Bit 0
(LSB)
Bit 1
Bit 2
Bit 3
Bit 4
Bit 5
Bit 6
Bit 7
(MSB)
Parity
Stop
(high)
The parity bit ("Even", "Odd", "None") can be set with the "Parity configuration" parameter.
The transmission speed is variable and can be set with the "Transmission speed" parameter.
1.2 Communication process
MODBUS over Serial Line Specification & Implementation guide V1.0 defines the following frame for the
transmission protocol:
Command from
master:
Response from fan:
Address
8 bits
Command
8 bits
Data
N * 8 bits
CRC H
8 bits
CRC L
8 bits
Start
> 3.5 char
Address
8 bits
Command
8 bits
Data
N * 8 bits
CRC H
8 bits
CRC L
8 bits
Start
> 3.5 char
Contrary to the general specification the maximum telegram length is 80 bytes.