ProSoft Technology PTQ-AFC - Manual (Page 82)

Quick Start PTQ-AFC ♦ Modicon Quantum Platform
User Manual Liquid and Gas Flow Computer for Hydrocarbon Products
Page 82 of 259 ProSoft Technology, Inc.
June 23, 2011
6.8.3 Virtual Slave
The module also provides a Virtual Address Space of 20,000 Modbus registers.
This address space is divided equally between the Input Register Bank (10,000
registers) and the Holding Register Bank Holding Register Bank (10,000). This is
where you can create a virtual re-map by cross-referencing any of the 130,072
Primary Slave Modbus registers to the 20,000 Modbus registers in the Virtual
Slave Banks, thereby making it easy for a SCADA Master to poll only the
necessary Modbus addresses in contiguous blocks. The virtual slave can also be
used for data polling from the processor through the backplane.
Modbus access to the Virtual Modbus Slave is disabled by default since its
Modbus address is originally set as 0. To use the Virtual Modbus Slave, you
must initially configure a Modbus address greater than zero in order to enable it.
Refer to Site Configuration for more information about enabling the Virtual Slave
and using the remapping feature. The PLC may always access the Virtual Slave,
whether or not it has a non-zero slave address and thus is available via Modbus.
A download operation will not transfer the Virtual Slave Remapping configuration.
You must click on the Write button on the Indirect Address Remapping dialog
box to transfer the data.
Note: The first 100 registers in the Virtual Slave Holding Register Bank have been pre-assigned
and cannot be remapped. They map directly to the first 100 holding registers of the Primary Slave.
Virtual Slave Example Application
Assume that an application requires a remote Modbus Master to poll the orifice
diameters for the first 5 channels. Continuing the previous example, the holding
register addresses are listed again the following table.
Meter Registers
1 8162 and 8163
2 10162 and 10163
3 12162 and 12163
4 14162 and 14163
5 16162 and 16163