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. Read More

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... Read More

Since the Dev Address field is a signed 16-bit integer, the maximum positive value accepted by RSLogix is 32767 However 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... Read More

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... Read More

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

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). Read More

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... Read More

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... Read More

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... Read More

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... Read More

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... Read More

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

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... Read More

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... Read More

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... Read More

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.... Read More

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... Read More

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... Read More

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... Read More

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