Comtrol IOLM Modbus TCP - Manual (Page 9)

IO-Link Master Modbus/TCP Reference Manual: 2000590 Rev. A Chapter 1. Modbus/TCP Interface - 11
Multiple Port Process Data (PDI and PDO) Access via Modbus TCP
Modbus Read/Write Access where:
• All PDI data can be read with one Modbus Read Holding Registers message.
• All PDO data can be read with one Modbus Read Holding Registers read message.
• All PDO data can be written with one Modbus Write Holding Registers message.
• Controller Read access:
- The PDI data from one or more ports may be read with one message. (i.e.: If addressing port 1, at
address 1000, ports one to four may be read in one message.)
- The PDO data from one or more ports may be read with one message. (i.e.: If addressing port 1, at
address 1050, ports one to four may be read in one message.)
- Partial PDI and PDO data reads are allowed.
- The length of the Read message can range from 1 to the total, configured PDI or PDO length for all
ports starting at the addressed port.
• Controller Write (Output) access:
- Only PDO data may be written.
- The PDO data for one or more ports may be written with one Write Holding Registers message.
- Partial PDO data writes are not allowed.
- The length of the Write message must be equal to the total of the configured PDO lengths for all ports
to be written. The one exception is that the data length of the last port to be written must be equal to
or greater than the device PDO length for that port.