The first step is to configure the MBE driver. This entails setting up Channel, Device and Poll record configurations. From the System Configuration select Configure/SCADA or click on the instrument on the toolbox. This brings up the SCADA Configuration dialog box – not shown.

411

In the Configured I/O Drivers text box should be the MBE – Modbus Ethernet v6.10 driver. If not, it needs to be installed. Click once on the MBE driver then click on the Configure… button. This brings up the MBE Driver Configurator as shown above.

CHANNEL CONFIG… Shown in the MBE Driver Configuration picture above is the configuration for Channel 1. Up to 8 Channels may be configured as shown by the Channel buttons. Each Channel has Definition settings associated with it. Click on the Setup button to view the Channel Communication Settings as shown below.

412

In the Error Handling frame are shown the defaults – no changes were made. In the MBE Parameters frame the Host computer IP address is entered. This IP address represents the 4-byte address of the computer that is running the MBE driver and is communicating to the slave recorders. Shown is IP address 127.127.1.1. Your IP address will be different! DHCP (Dynamic Host Configuration Protocol) is not supported. The Advanced… button brings up the Channel Backup Communication Settings dialog. This would be used where a backup Ethernet card is used to continue communications in the event of primary Ethernet card failure. Click the OK button when done.

DEVICE CONFIG… Next to be configured are the Device settings for the Channel. The default Device Name of D11 was deleted and a Device Name of ‘FRODO’ has been added.




The Addressing Type must be set to 6 digits. the address map of data within the recorders is from 0 to 65535 (FFFFhex). These addresses represent the ‘x’ part of the 3x (Input Registers) and 4x (Holding Registers) Modbus address space. This is why the addressing type must be set to 6 digits. 

In the Primary Device frame the Primary Station Device IP address box represents the IP address of the  recorder. Here it is shown as 127.127.1.2. Your IP address will be different. The Port box provides the port number on which the hardware can provide network services. The Primary Bridge Destination Index box enables the specification of the identification number of a Modbus Plus to Ethernet bridge. These two fields should not require modification.

The Backup Device frame enables similar parameter entries as those for the Primary Device but for the backup Ethernet card if any.

Before discussing the POLL configuration, a few words on Modbus addressing… All data addresses in Modbus communication messages are referenced to zero (0). Input and Holding registers are referenced at 300001 and 400001 (for 6-digit addressing) respectively but are addressed as register 00000 in the data address field of the communications message. The means that for recorder data types of scaled (16-bit signed integers) the register type must be prefaced and one (1) must be added to the address.

POLL CONFIG… The Poll Record dialog box enables entry of individual poll records. Typically these will be block reads of data at a defined starting address from the recorder.

In the Poll Record dialog box shown below are two (2) poll records. The first poll record has been configured to read the first 6 channels in the recorders run-time data area whilst the second poll record reads those same 6 channels but from the recorders IEEE run-time data area.

413

Each channel in the either the integer or IEEE run-time data area consists of the current Process Value (PV), Status and Alarms – contiguously addressed as shown in the tables below. Therefore, the channel process values are not contiguously addressed and the polled record shown includes the 2 additional parameters from each channel, hence the Length of 18 and 24 in words. Note also the Data Type of Signed for integers and CFloat for IEEE values. None of the other poll record attributes have been changed.

417

POLL Record 1… The Channel 1 current Process Value (PV) is at address 41433 in the recorder This represents the ‘x’ part of the Modbus Input and Holding register address therefore, the Start Modbus address would be 441434 – essentially adding 400001 to any integer address listed in the manual. Now, when the request is made to read 441434, the leading four (4) represents a Holding register and since the data address field is referenced from zero, the address in the Modbus communications request is 41433 (A1D9hex). You can see this if you monitor the communications using Mission Control.

The Length is equal to 3 words per channel times 6 channels. The Data Type of Signed is needed as the PV is returned as a signed integer. This does not effect the Status or Alarm data as they do not use the sign bit (bit 15).

POLL Record 2… The addressing for IEEE values does NOT require 1 to be added to the address in the recorder. This is because the IEEE values are 2 words in length where the first word is at ‘address – 1’ in the recorder. With a Poll record Start address of 463684, the leading four (4) represents a Holding register and Modbus address 63684. Since the data address field is referenced from zero the Modbus communications request would be 63683. This satisfies the ‘address – 1’ requirement. The block length is for 24 words because the PV is 2 words and the Status and Alarm are 1 each as shown in the table below.


The Length is 4 words per channel times 6 channels. The Data Type is CFloat. This tells the MBE driver that the word order received from the recorder is reversed. This is important because the IEEE standard for binary single format consists of a 1-bit sign, an 8-bit exponent and 23-bit fraction as shown in the table below. If set to Float, the value displayed would be incorrect as Float decoding depends on the proper order of the 2 returned words.

418

This completes configuring the MBE Driver.

TAG Configuration… The next step would be to create Tags in the database. The Database Builder window is shown below and contains 6 tags – all AI Type – for the integer PV values and 4 tags for the float PV values. Note that for the integer PV’s the I/O address have 400001 added to that value listed in the manual while the real PV’s have 400000 added 

414

Scaling can be carried out for the integer PV’s if necessary. Scaling is not required for the IEEE values. Know that the integer value returned from the recorder will contain an implicit decimal point position based on the Max Decimal Digits found in the Channel configuration. You can see from the Database Builder above that the CH2 and CH4 integer values have not been scaled and are off by a factor of 10 from the CH2R and CH4R IEEE values.

Channel 1 (CH1) as shown above was configured with a Max Decimal Digits of 1 in the recorder. In order for it to be scaled, the Signal Conditioning in the Hardware Specifications frame must be changed from NONE to LIN. This enables the Low Limit and High Limit in the Engineering Units frame. The limits are the 16-bit unsigned maximum value (+/- 32768) divided by 10 that results in the values shown.

415

Channel 1 (CH1R) AI as a Float is shown below. Only the Hardware Specification frame boxes were changed. The Engineering Units frame values have no effect on the displayed value.

416

Leave a Reply