Modbus is probably the most widely used protocol in process control industries today. Modbus allows serial communication to occur between slave devices such as Programmable Logic Controllers (PLC’s) and  Instrumentation and Master devices such as computers or Digital Control Systems (DCS’s). The Modbus protocol has two basic forms. The RTU or Binary form and the ASCII form. In RTU or binary form all the bytes transmitted in binary a binary format. Hence the protocol is more efficient and faster. ASCII on the other hand all the bytes are transmitted in the ASCII characters ‘0-9’ and ‘A-F’.

The slave has 4 different types of internal variables that can be accessed by the master.

• Coils which are digital bits that can be read and written to. They are numbered from 00001 to 09999
• Input Status which are digital bits that can be read. They are numbered from 10001 to 19999
• Input Registers which are 16 bit integers that can be read. They are numbered from 30001 to 39999
• Holding Registers which are 16 bit integers that can be read and written to. They are numbered from 40001 to 49999
  

Modbus has a number of different functions. The most commonly used functions which ModbusView uses and responds to are

• Function 1 is  Read Coil Status
• Function 2 is Read Input Status
• Function 3 is Read Input Registers
• Function 4 is Read Holding Registers
• Function 5 is Write to a Coil
• Function 6 is Write to a Holding Registers
• Function 15 is Write to Multiple Coils
• Function 16 is Write to Multiple Holding Registers

For a more detailed explanation of the Modbus protocol the user is advised to obtain and read the Modbus standard from Modicon. This is on available on the Web Site www.modbus.org

FEATURES OF MODBUS VIEW
ModbusView is an easy to use Modbus simulation program that can operate on a PC under Windows 98, ME, NT, 2000 and XP. The ModbusView program is extremely powerful in that it allows your PC to simulate both a Master and a Slave. It can communicate both in the RTU form and the ASCII form and it can also be set to a range of baud rates, data bits, parity and stop bits. With ModbusView you can fully test out your Human Machine Interfaces (HMI's or MMI's), instrumentation operations and PLC communications and operations.

With the PC simulating a master the user can

• read the status of coils in a slave device connected to the PC
• read the input status in a slave device connected to the PC
• read the value of input registers in a slave device connected to the PC
• read the value of holding registers in the slave device   connected to the PC
• read the values in the input and holding registers as integers (Decimal or Hexadecimal) , long integers (Decimal or Hexadecimal) and Floating point.
• manipulate or alter the coils and holding registers in the slave device connected to the PC

With a PC simulating a slave device the user can

• respond to queries and commands from the Master connected to the PC
• view the status of coils in the slave
• view the input status in the slave
• view the value of input registers in the slave
• view the value of holding registers in the slave.
• view the values in the input and holding registers as integers (Decimal or Hexadecimal) , long integers (Decimal or Hexadecimal) and Floating point.
• manipulate or alter the input status, coils, input registers and holding registers in the slave
• can simulate up to 5 slave devices at once allowing you to simulate a large system

To make life even easier the configurations of the Master and Slave and the contents of the coils, input status, input and holding registers can be saved to disk. Hence when you want to try out a number of different scenarios you don't have to enter the same initial data all the time or when you finish for lunch or  the day   you can resume as you left it.

HOW TO DOWNLOAD AND BUY MODBUS VIEW
Download a copy of the unregistered program from this site. The unregistered version of MODBUS VIEW has all the features of the registered version except there is a time limit of 15 minutes. After 15 minutes you have to restart the program. This will allow you to trial the program before buying.

Download ModbusViewV143.zip Version 1.43 (Updated 25 March 2009)

All prices are in Australian Dollars. Prices do not include GST (Goods and Services Tax). 10% GST applies to goods delivered in Australia. Australian GST is not paid on shipments despatched to an international destination. You can check the exchange rate by going to http://www.x-rates.com

ModbusView Software Price: AUD$85.00

On payment of AUD$85.00 you will be issued with a serial number and registration number.