Ethernet Modbus Master Service - GE Mark VIeS System Manual

9.1.2.5 Ethernet Modbus Master Service

The PSCA can use one of its two Ethernet ports to support the Ethernet Modbus Master Protocol. This configuration can only
be used with a simplex network. The Ethernet IP address for Modbus can not be included in the range of the IONet submask
range. All Ethernet Modbus stations are configured on Port 7 through the ToolboxST application. The Ethernet Modbus
implementation follows the Open Modbus/TCP Specification for a Class 1 device.
The ToolboxST application allows up to 18 Ethernet Modbus stations to be attached to the PSCA. The CPU loading for each
station varies depending on the number of Modbus registers being requested and the update rate. Also, the field device
connect and data response rate may vary. Data throughput should be validated in system test when multiple stations and/or
large amounts of data are being transferred.
The following parameters are defined for all stations on the PSCA Ethernet port:
• TCP/IP address for PSCA Ethernet port
• TCP/IP subnet mask
• TCP/IP Gateway IP address of intermediate router (optional)
The following parameters are defined for each field device station:
• Field device TCP/IP address
• Field device TCP/IP port (Modbus default is 502)
• Modbus Station address (optional)
• TCP/IP Read time-out (default is 1s)
Note On initial wait for each Slave device response to a Modbus request, the PSCA will re-try its receive for up to six
times for an effective time-out period of (6 * TimeOut) = Total timeout before indicating No Response and proceeding to
the next message. After three No Responses have occurred, the connection will be closed, and the PSCA will periodically
attempt to re-establish communications.
• 32–bit data Word ordering (for example, LSW or MSW first)
Note First denotes which word is in the lower-numbered register. All 16-bit registers are Big-Endian per standard
Modbus convention.
• Open Modbus/TCP IP protocol
The Modbus service is configured at the signal level as follows:
• Signal type
• Register number
• Read/write
• Transfer rate, 0.5, 1, 2, or 4 Hz
• Scaling: Raw min/max, Eng min/max
The service supports function codes 1-7, 15, and 16. It also supports double 16-bit registers for floating point numbers and
32-bit counters. It periodically (10 sec) attempts to re-establish communications with a dead station.
Type casting and scaling of all I/O signals to/from engineering units are supported on the PSCA and the ToolboxST
application, for both fixed I/O and Modbus I/O.
PSCA Modbus Master (Serial Communication) Module
Public Information
GEH-6855_Vol_II System Guide 289