| Parameter | Meaning | Unit | Default value |
|---|
| Maximum count of request retries. If no reply returns after a request had been sent, the station will be in the status of a communication error. | s | 2 |
| Timeout before resending a request if no reply had not received. | s | 0.1 |
| Delay after sending the request before reading the response. | s | 0.1 |
| Timeout between reading the reply. | s | 0.1 |
| Maximum The maximum number of retries of the reply reading. | - | 20 |
| "Start silent interval" before the beginning of the transmission in RTU mode. | ms | 50 |
| "Stop silent interval" after ending of the transmission in RTU mode. | ms | 50 |
| Byte order in Little-endian mode for 4-byte variables. The individual options indicate in which bytes (1-lowest, 4-highest) the individual bytes from the communication will go: - 2143 - first the lower word is received, then the higher word (higher byte within the word is always first)
- 3412 - first the higher word is received, then the lower word (lower byte within the word is always first)
- 1234 - bytes are received from lowest to lowest (opposite of big-endian)
| - | 2143 |
| Special byte mode of transmission in which the values of registers have a length of 1 byte and not 2 bytes as it is defined in Modbus protocol specification. | YES/NO | NO |
| Special variable mode of transmission in which the values of registers have variable lengthlengths. Setting The setting of Variable mode:
Little endian = the lowest bytes are sent first
Big endian = the highest bytes are sent first
OFF = variable mode is switch switched off Note 1: Variable and byte mode are incompatible and only one of them can be enabled.
Note 2: Emerson FloBoss 103 device: text strings and time stamps of 6-byte are sent always from the lowest byte.
Note 3: Variable mode is implemented only for Protocol Mode=RTU.
Note 4: A data encoding big-endian is used automatically, according to the default parameter values Byte mod=NO and Variable mode=OFF (i.e. according to MODBUS protocol specification). | OFF
Little endian
Big endian | OFF |
| Log Logging of another detailed debug information about communication on in the line log. | YES/NO | NO |
| Protocol mode: RTU or ASCII. Note: In case of "MODBUS over TCP/IP", the parameter value is ignored and Protocol Mode=RTU is used. | RTU
ASCII | RTU |
| Sets an address model of MODBUS protocol:
MODBUS PDU data are addressed from 0 up to 65535.
MODBUS data Model data are addressed from 1 up to 65536.
Note: MODBUS PDU is a default value. If the MODBUS data Model is set, the object with the address X is addressed as X-1 in MODBUS PDU.
After you change this parameter, restart a proper communication process. | MODBUS PDU
MODBUS data Model | MODBUS PDU |
| Select a variant of the protocol in case of TCP/IP communication:
"MODBUS TCP" is a variant of communication without control checksum. Safeguarding is done by the underlying TCP protocol.
"MODBUS over TCP" is a variant where a payload is MODBUS RTU data containing a checksum. | "MODBUS TCP"
"MODBUS over TCP" | "MODBUS TCP" |
| Maximum count of registers that are read by one request. | - | 100 |
| Maximum count of bytes that are required by one request (only in "Byte mode"). | - | 100 |
| To read the values from addresses that are not configured is not allowed. Description and example:
The requests for data, which are limited by protocol parameter "Max. Registers" or "Max. Bytes", are sent as standard. If I/O tags with addresses "Holding Registers" 1, 2, and 5 have been configured, one request reading 5 registers starting with the address 1 is sent although the I/O tags with addresses 3 and 4 are not configured. It is more efficient to obtain the required data by one request than by two ones even if the unnecessary data are also read.
If the parameter "Skip Unconfigured" is set on YES, two requests are sent, the first one reads two registers from address 1 and the second one reads one register from address 5. | YES/NO | NO |
| If this parameter is set to YES, then an extra check is performed when receiving a response to a read request: the length of received data is checked whether it matches the number of registers in a read request:- if Byte mode is on (Byte mode=YES), length of received data must equal to the number of registers
- if both Byte mode and variable mode are off, length of received data must equal to double of the number of registers
- if the variable mode is on (Variable mode=little-endian or big-endian), check has not been implemented yet
This extra check is reasonable on high-latency and variable-latency lines - e.g. GPRS networks - to detect and avoid the situation when read request (#1) is repeated due to timeouts and then two responses are received, the second of which could be considered to be an answer to another read request (#2), thus causing wrong values being assigned to I/O tags addressed by this read request #2. | YES/NO | NO |