Modbus

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What Modbus address would we need to put into the MODSIM32 simulator if we specified on the MVI56-MCM device address to 8680HEX (-31104 decimal) when the MVI56-mcm is the slave?

The negative value display on the ControLogix is due to the format of the data, 15bits +one sign bit. Set a value of 34432 into MODSIM32. Use a calculator to convert the value from 8680 hex to decimal, 16bits = 34432....

If I am reading the value from ProSoft 4x register, and it represents a digital input or digital output, how is the value stored?

Each digital point coming from the drive will be placed in an integer register in the ProSoft module. So a digital 0 will be an analog 0 (0x00), and a digital 1 will be an analog 1 (0x01)....

How do I enter a Modbus address of 40001 or higher in the DevAddress command field of my MVI56-MCM?

Since the Dev Address field is a signed 16-bit integer, the maximum positive value accepted by RSLogix is 32767However the Dev Address field is a Modbus offset value. When using a Modbus function code 3, 6, or 16, an address base of 40001 is assumed. The Dev Address field is an o...

Why is the bit or coil level data incorrect?

Bit read and write commands are issuing properly, and responses are coming from the slave(s), but the data is not correct.When setting the intaddress field for a bit or coil Modbus command (Modbus function codes 1, 5, and 15), the internal address specified in the command must be...

Defining the Slave ID when issuing Modbus Broadcast write commands

All Modbus master modules (MVIXX-MCM and ProLinx MCM) slave id for Modbus broadcast command must be set to 0....

I need to connect more than one Modbus master devices to the same Modbus slave device.

The Modbus master devices are connected to the 3 Modbus slave ports of the ProLinx module. The Modbus slave device is connected to the Modbus master port of the ProLinx module. You can increase the number of master devices connected to the same slave device using the cascade arch...

Do any Prosoft modules support Modbus UDP?

Prosoft does not currently offer any UDP based Modbus solutions, all modbus solutions offered via Ethernet are Modbus TCP/IP only....

I have multiple Modbus masters that need to communicate with 1 or more Modbus serial (RTU) slave devices. What product should be used??

The best option (straightforward implementation, most flexible option) would be the PLX31-EIP-MBS4 or the PLX31-MBTCP-MBS4.These gateways have four configurable serial ports that will allow data from 1 or more Modbus serial slave devices to be shared with multiple masters....

I am trying to use a ProSoft Modbus solution to send/receive data to a MSA Ultima X gas dectection system with Modbus interface and am having problems. How can I resolve this issue?

The MSA UltimaX gas detectors have a Modbus interface implementation that is within the limits of the Modbus protocol specifications but is somewhat different than more conventional Modbus communications implementations by other manufacturers. Therefore, how you access...

How can a module's Modbus port, configured as a Slave port, detect communication loss with the Master port?

When a device is a Modbus slave, it has no way to tell the difference between a situation where communications have failed between it and the master and a situation where the master is not trying to talk to it. If our module does not see a request from the master, it will not kno...

Can Modbus support redundant masters?

The Modbus protocol does not support redundant masters, however ProSoft has had customers setup a redundant Modbus network using the inRAX MVI46-MCM, MVI56-MCM, MVI71-MCM, 3100-MCM, and 3150-MCM modules. Only ProSoft products that support configuration through ladder logic can be...

I have limited or no experience with Modbus. How can I find out more about the protocol and command structure?

Watch our Modbus tutorial video:http://www.youtube.com/watch?feature=player_embedded&v=k993tAFRLSE Download the Modbus specification:http://www.modbus.org...

I have a ProSoft Modbus Master solution and would like to know, is the Slave Status List the best place to monitor for communications health of the network?

The Slave Status list is merely a 'scratchpad' area the Modbus Master firmware uses to keep track of its current poll state with respect to a particular Slave. The Slave Status List is not the best place to monitor the health of communications between a ProSoft/ProLinx Modb...

What's the difference between Modbus ASCII and Modbus RTU?

The original Modbus specification included two possible transmission modes: ASCII and RTU. Modbus RTU mode is the most common implementation, using binary coding and CRC error-checking. Modbus ASCII messages (though somewhat more readable because they use ASCII characters) is les...

Read Commands from my Modbus Master to a ProSoft MCM Slave are working but Write Commands are failing. How do I fix this?

When a MCM module has a port set up as a Slave, especially if there are other Slaves on the same physical network, the Modbus Master may have trouble sending Write Commands to the MCM Slave port. In these cases, the Read Commands alway execute successfully; but the Write Commands...

How do I read/write Modbus binary data?

In a Modbus system, bit-level data is referred to as either "Coils" (read/write bit-level data) or "Input Status" (read only bit-level data.) The Modbus protocol uses Function Codes in commands to specify both the action (read or write) and data object (input ...

How do I monitor the health of coms to my slaves when the module is a Master?

When the MCM driver is setup to be a Modbus master, the firmware will maintain a list of status codes. Each number in the "master commman error" list corresponds to a single message in the master command list. The position of a given status code matches the position of ...

How do you detect the individual Slave failure?

To detect the slave failure, you may use the command error list. Each command returns an error code once it is executed. If a command returns a value different of 0, this means that there was a problem during the command execution. The command error list can be found in the read ...

How can I detect the feedback status of individual command successful or failed?

Each command returns an error code once it is executed. If a command returns a value different of 0, this means that there was a problem during the command execution. The command error list can be found in the read data zone at the address you specified in mcm.port1.cmderrptr....

What are the causes of a -11 error code using a ProSoft Modbus product?

A -11 is a timeout error. The MCM master port is sending the command but it does not get a valid response from the slave back in time. If the port x Response Timeout setting is 1000ms, the port x LED will blink once every 1000ms. This indicates the co...

My RX light is on solid, what might that indicate?

If the RX light is on solid on your modbus serial port and:The port is in RS485 mode- This is usually indicative of polarity being reversed (ie. positive is connected to negative instead of positive to positive). Try swapping the wiring to pins 1 and 8 on our port.The port is in ...

Why are my PLX gateway modbus serial commands not executing despite being enabled?

If your modbus serial port and its commands are both enabled, but the commands do not appear to even be executing (status shows no requests are being made, data analyzer shows nothing coming out of the port, etc.) check the value of Command Control Reg. Command Control Reg is loc...