This discussion assumes you want the Babel Buster SPX to be the Modbus Master (most common use). Let's review the setup procedure for a single Modbus read map. We suggest starting with one register. Once you get that working, proceed to fill up the table.

First, go to the Local Device page and make sure you have the baud rate set, and parity (if any) selected. If you do not know what baud rate your Modbus device is set to, consult that manufacturers documentation before proceeding.

Make sure the Master button is clicked. Start with a liberally slow timeout, like 0.5 second just to be rather certain you do not have timeout problems. (We have yet to see a piece of working equipment take longer than half a second to respond to a Modbus master.)

Next, go to the RTU Read Map page (below) and click the "1" in the left column. This takes you to the expanded view of map #1.

To get started, you must enable some maps. Enter a number greater than zero in the # RTU Read Maps Enabled window at the bottom of the expanded view page (below) and click Update.

Next, select a register type, a register number, a unit # (aka slave ID or slave address), and a local register number to store the data in. If any of the red check marks shown below are "none" or zero, you will get no action even attempted. Make sure the Unit # (slave ID or slave address) matches whatever you have your Modbus device set to. If you are uncertain what address it is set to, you need to consult the manufacturer's documentation for that equipment before proceeding.

The following example shows the only non-zero entries required to successfully read holding register #1 from unit #1 and store the data in local register #1. Once these (or comparable) entries have been made, click the Update button.

At this point, you can go to the data page (below) and see if you have data showing up. If you get no data, there is a problem. The confirmation that you are probably getting no data is the "time since last update". In this example, we see 126 seconds have elapsed. We are attempting to update every 2 seconds, so obviously data retrieval is not happening.

If you are getting no data, check the Error Codes page (below). Here we see that the "No Responses" is about equal to the "Total Messages". This means we are not getting anything back from the Modbus slave. If you are certain all of the above setup is correct, the only conclusion you (or we) can come to at this point is that there is a wiring problem, or the slave is not responding or not configured correctly. Review wiring information, and check the slave configuration.

Here is what the LED indicators will tell you:

Yellow LED on Ethernet Connector: Should remain on any time you have a link. If the SPX is powered up, and has been for at least a minute, but you see no yellow LED, check your Ethernet cable, switch/hub, etc.

Green LED on Ethernet Connector: Will flash each time the Ethernet interface sees traffic on the network (regardless of whether addressed to the SPX).

The three LEDs next to the screw terminal plug indicate Modbus RTU traffic.

Modbus RTU is a Master: The yellow LED will flash every time SPX sends a request (or command) to a slave. Each yellow flash will be followed by either a green or red flash. The green LED means a good response was received from the slave. The red LED means any of several things: (a) No response was received, (b) An exception error was received, (c) A checksum error was found in the response. Check the Error Codes page to see which it is.

Modbus RTU is a Slave: The yellow LED will flash every time SPX receives a request (or command) from the master. If SPX responds with a good packet, the green LED will flash. If the master requested something that is an error, or a checksum error was found in the packet, the red LED will flash.

If you are unsuccessful in getting RTU traffic, try switching the TX+ and TX-, especially if the Modbus device is labeled A and B. The chip manufacturers and Modbus spec writers document A and B opposite of each other.

There is a green power LED inside the SPX. You can see its reflection between the terminal block LEDs and the RJ-45 Ethernet jack.