Starting up the SPI 3
14
Trebing & Himstedt | SPI 3 | MODBUS RTU
SPI 3 Configuration
The configuration telegram consists of the »MODBUS_Master_Kopf« or
»MODBUS_ Kanal« module and further modules for the respective I/O fields
listed in the table.
Always start with the »MODBUS_Master_Kopf« module (standard use) or
»MODBUS_ Kanal«.
After module selection, you need to set the parameters specific for this module (see
»SPI 3 Parameters« on page 15).
Now you can use the modules listed in the table (SPI 3 Release 15 and higher).
Note!
You can insert a maximum of 33 modules (1 »MODBUS_Master...« and 32
»MODBUS_REG_...«). A maximum of 244 input bytes and/or 244 output
bytes can be used. The total number of input and output bytes must not
exceed the value of 256 bytes (memory limit in the SPI 3).
Observe data consistency when using I/O fields bigger than 2 words
(depending on PLC used).
The SPI 3 always sends data for all configured modules in full length to the
MODBUS slave. Module MB_REG_Write_1B is an exception. You can use
Module Name
I/O Field
Description
MODBUS_ Kanal
4 words
Specific SPI 3 parameters, 4-word data channel.
Data channel can only be used in connection
with function blocks.
MODBUS_Master_Kopf
–
Specific SPI 3 parameters, no data channel.
MB_REG_WRITE_1B
1 byte
Specific module parameters such as function
(read/write) and size of the part to be depicted
from the MODBUS register of the field device
(see figure on page 13).
You can set the different MODBUS functions for
the selected module through parameterization
(see next chapter).
MB_REG_WRITE_1W
1 word
MB_REG_WRITE_2W
2 words
MB_REG_WRITE_4W
4 words
MB_REG_WRITE_8W
8 words
MB_REG_WRITE_16W
16 words
MB_REG_READ_1B
1 byte
MB_REG_READ_1W
1 word
MB_REG_READ_2W
2 words
MB_REG_READ_4W
4 words
MB_REG_READ_8W
8 words
MB_REG_READ_16W
16 words
