This discussion assumes you want the Babel Buster SP 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.

Check the DIP switches on your Babel Buster SP. If using RS-485 (EIA-485), switches 1 and 2 should be down, 3 and 4 should be up. You do want termination at the Babel Buster SP (unless you have several on the same Modbus RTU network, which will not work if they are all configured as Master).

This view is of the male connector looking into the Babel Buster SP. The female connector orientation will be opposite. Note: This is NOT a PC COM port. Connection for Half-Duplex (2-wire RS-485): Connect TXD+ to RXD+ on the SP, and these to the "+" on your Modbus device. Connect TXD- and RXD- on the SP, and these to the "-" on your Modbus device. If your device's RS-485 terminals are marked A and B, with no indication of + or -, just guess. There is about a 50% chance it is marked wrong anyway. Modbus protocol specifications and RS-485 driver chip specifications are opposite each other in their use of A and B. If you are uncertain about the +/- A/B thing, and you are not getting any response, try swapping the wires. You will not do physical damage by reversing RS-485 wires. Many times simply swapping the wires fixes the problem.