More and more people are using Modbus to get data from their instruments and controllers back into their control systems for reporting, alarming and troubleshooting.
And while I can’t be there to help you set up your Modbus master, I can give you 13 rules and some general practice advice for communicating to any Modbus RTU device.
I’ll even throw in some specifics for Modbus RTU connections to the RM7800 flame safety controllers.
Download this whitepaper and give it a read: A Baker’s Dozen Rules for Modbus RTU and Honeywell RM7800s
It’s chock full of technical nitty gritty because with any communications protocol, the devil is in the details. It’s ALL nitty gritty. Get one detail wrong and your Modbus link is either silent or talking garbage.
If you have any Modbus RTU tips for Honeywell RM7800 flame safety controllers, please share them below. I’d love to expand the list to make it a fully comprehensive guide.
Lesman Tech Tips 
#1 by Justin on June 23, 2016 - 11:46 am
Hi Dan –
Question about the modbus addressing on the S800A – All of the manuals say to go to the display setup in order to set the modbus address and parameters; but scrolling up and down doesn’t get me to any display setup screen. Tried all different button combinations. Any advice?
#2 by danstips on July 1, 2016 - 8:18 am
If the Modbus address selection does not appear on a S7800A, then that particular display is probably an early firmware version that does not support Modbus.
See the bottom of page 2 of the app note (link below) for graphics showing location of the firmware rev number.
Click to access lesman-bakers-dozen-tips-modbus-rtu-honeywell-rm7800s.pdf