# Modbus Addressing AB Micro850 **URL:** \ **Category:** Ignition\ **Created:** [August 2, 2018, 12:48pm UTC](https://forum.inductiveautomation.com/t/modbus-addressing-ab-micro850/19070 "2018-08-02T12:48:48Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![dkhayes117](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/dkhayes117/32/68344_2.png) [@dkhayes117](https://forum.inductiveautomation.com/u/dkhayes117)\ **Post date:** [August 2, 2018, 12:48pm UTC](https://forum.inductiveautomation.com/t/modbus-addressing-ab-micro850/19070/1 "2018-08-02T12:48:48Z")
I’m trying to setup a couple of tags in an AB Micro850 PLC referencing this[thread](http://forum.inductiveautomation.com/t/allen-bradley-micro850/6676). However I’m lost on the setup. I’ve never used Modbus before. Below is a snapshot of the plc program, I want to start off with a tag to show if the machine is on or off which I think reading set coil \_B001 is what I want?? I tried addressing it in ignition tag as [WoodChipper]C000001, but nothing. ![](https://us1.discourse-cdn.com/inductiveautomation/original/2X/2/2a12d212369fcde6792bfb9b64ae5838fa445263.png) Any help is appreciated ---
**Author:** ![dkhayes117](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/dkhayes117/32/68344_2.png) [@dkhayes117](https://forum.inductiveautomation.com/u/dkhayes117)\ **Post date:** [August 2, 2018, 12:55pm UTC](https://forum.inductiveautomation.com/t/modbus-addressing-ab-micro850/19070/2 "2018-08-02T12:55:14Z")
![](https://us1.discourse-cdn.com/inductiveautomation/original/2X/3/3d6ac196bdd5f2c29199b73edfc22baf48d90774.png) I just found this in the PLC software, not sure whether this is needed to map the addresses? ---
**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\ **Post date:** [August 2, 2018, 1:11pm UTC](https://forum.inductiveautomation.com/t/modbus-addressing-ab-micro850/19070/3 "2018-08-02T13:11:04Z")
Yes, you have to map each variable you want to access via Modbus. ---
**Author:** ![dkhayes117](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/dkhayes117/32/68344_2.png) [@dkhayes117](https://forum.inductiveautomation.com/u/dkhayes117)\ **Post date:** [August 2, 2018, 1:12pm UTC](https://forum.inductiveautomation.com/t/modbus-addressing-ab-micro850/19070/4 "2018-08-02T13:12:29Z")
I’ll give it a shot after machine shut down ---
**Author:** ![dkhayes117](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/dkhayes117/32/68344_2.png) [@dkhayes117](https://forum.inductiveautomation.com/u/dkhayes117)\ **Post date:** [August 3, 2018, 12:25pm UTC](https://forum.inductiveautomation.com/t/modbus-addressing-ab-micro850/19070/5 "2018-08-03T12:25:32Z")
I was able to map the variables and upload it to the PLC. It worked well, I thought this was going to be more complicated but was actually pretty simple. thanks ---
**Author:** ![james.wilson](https://avatars.discourse-cdn.com/v4/letter/j/53a042/32.png) [@james.wilson](https://forum.inductiveautomation.com/u/james.wilson)\ **Post date:** [October 15, 2020, 9:19pm UTC](https://forum.inductiveautomation.com/t/modbus-addressing-ab-micro850/19070/6 "2020-10-15T21:19:39Z")
I am able to connect to a Micro850 using the Modbus TCP protocol but I can’t get values from it. I have the Modbus Mapping setup in the PLC as shown here: ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/e/4/e4ab81e137e6396e0c0443551be3e8d1ab7271e1.png) I have tried many different names in the OPC Item Path. Note: The tag names in pic below match the name used in the OPC Item Path, so you can see I’ve tried many names in desperation. I would think HR1 would work though. ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/0/b/0b522f5dbe19bdb65aed0965e5aa1ccccbedd010.png) I don’t know how to determine if this problem is on the PLC side or Ignition side. Can anyone suggest how to determine the cause of my problem? Oh, please ignore that the Tag Browser is showing “Connecting” when I took the screen print, we turned the PLC off at the time but Ignition does show Connected when the PLC is on. ---
**Author:** ![Matrix\_Engineering](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/matrix_engineering/32/19781_2.png) [@Matrix\_Engineering](https://forum.inductiveautomation.com/u/Matrix_Engineering)\ **Post date:** [October 15, 2020, 10:51pm UTC](https://forum.inductiveautomation.com/t/modbus-addressing-ab-micro850/19070/7 "2020-10-15T22:51:05Z")
Did you enable ModbusTCP in CCW? (As per the little warning top right of your first image) ---
**Author:** ![Matrix\_Engineering](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/matrix_engineering/32/19781_2.png) [@Matrix\_Engineering](https://forum.inductiveautomation.com/u/Matrix_Engineering)\ **Post date:** [October 15, 2020, 10:53pm UTC](https://forum.inductiveautomation.com/t/modbus-addressing-ab-micro850/19070/8 "2020-10-15T22:53:31Z")
> [@james.wilson](#): > > I don’t know how to determine if this problem is on the PLC side or Ignition side. Can anyone suggest how to determine Use ModPoll or similar software to rule out Ignition as a start ---
**Author:** ![james.wilson](https://avatars.discourse-cdn.com/v4/letter/j/53a042/32.png) [@james.wilson](https://forum.inductiveautomation.com/u/james.wilson)\ **Post date:** [October 16, 2020, 2:58pm UTC](https://forum.inductiveautomation.com/t/modbus-addressing-ab-micro850/19070/9 "2020-10-16T14:58:35Z")
Yes, Modbus TCP was enabled or Ignition wouldn’t be able to connect to it. ModPoll was helpful. I found that having a single invalid tag pointing to a Modbus address in Ignition was causing my good tags from getting data from other Modbus addresses. Once I disabled all my tags where I was using trial and error, I enable a single tag and it worked. ---
**Author:** ![Pat](https://avatars.discourse-cdn.com/v4/letter/p/8491ac/32.png) [@Pat](https://forum.inductiveautomation.com/u/Pat)\ **Post date:** [August 31, 2022, 3:18am UTC](https://forum.inductiveautomation.com/t/modbus-addressing-ab-micro850/19070/10 "2022-08-31T03:18:12Z")
> [@james.wilson](#): > > I found that having a single invalid tag pointing to a Modbus address in Ignition was causing my good tags from getting data from other Modbus addresses. I encountered an issue similar to this today. I was able to access some Modbus registers in the Micro850, but when I started trying to access additional Modbus registers all my existing working tag values went to Bad. The problem was that the registers in the Micro850 were not in a continuous block and if you request a Modbus register from the Micro850 that is not configured, it will return an Error. By default the Ignition Modbus driver has Span Gaps turned on, which was causing Ignition to request registers that were not in the Micro850, to which the Micro850 return Error and then all my previously working tag values went to Bad. Once I realized what was going on, I disabled Span Gaps and all the tag values started working correctly. ---
**Author:** ![james.wilson](https://avatars.discourse-cdn.com/v4/letter/j/53a042/32.png) [@james.wilson](https://forum.inductiveautomation.com/u/james.wilson)\ **Post date:** [September 1, 2022, 3:19pm UTC](https://forum.inductiveautomation.com/t/modbus-addressing-ab-micro850/19070/11 "2022-09-01T15:19:22Z")
Thank you for this update! ---
**Author:** ![Logan\_Chance](https://avatars.discourse-cdn.com/v4/letter/l/df705f/32.png) [@Logan\_Chance](https://forum.inductiveautomation.com/u/Logan_Chance)\ **Post date:** [September 15, 2023, 4:18pm UTC](https://forum.inductiveautomation.com/t/modbus-addressing-ab-micro850/19070/12 "2023-09-15T16:18:19Z")
Has anyone had no errors connecting, values appear in the tag browser, but the values for the float be incorrect? First time trying to get modbus communicating. I probably am misunderstanding the radix and modbus address during the setup on the gateway... I did have to start the modbus address at 2 instead of 1 or else all the values bounce around. ![Micro850 Modbus 1](https://us1.discourse-cdn.com/inductiveautomation/original/3X/7/7/77e6cee8a451e1f716c62a9bd96efcbe9387acce.png) ![Micro850 Modbus 2](https://us1.discourse-cdn.com/inductiveautomation/original/3X/3/8/38658d8c7166cec56cb588d9be2760bedff419f0.png) ![Ignition Modbus](https://us1.discourse-cdn.com/inductiveautomation/original/3X/9/f/9fb8bf70f72218b6c26a8934255b96d13ec6ad02.jpeg) ![Ignition Modbus 2](https://us1.discourse-cdn.com/inductiveautomation/original/3X/d/0/d04e609e4025c4d77b80a4b1dc193f401505df69.jpeg) ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [September 15, 2023, 4:20pm UTC](https://forum.inductiveautomation.com/t/modbus-addressing-ab-micro850/19070/13 "2023-09-15T16:20:19Z")
Some combination of setting zero-based addressing and/or swap words should work for you (in the device advanced settings on the Ignition side). ---
**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\ **Post date:** [September 15, 2023, 5:15pm UTC](https://forum.inductiveautomation.com/t/modbus-addressing-ab-micro850/19070/15 "2023-09-15T17:15:13Z")
FWIW, if you do much with this family of processors, you might want to look at my latest EtherNet/IP driver. (So you don't have to set up Modbus in the ML8xx.) > [@Automation Professionals' EtherNet/IP Communication Suite V2](https://forum.inductiveautomation.com/t/automation-professionals-ethernet-ip-communication-suite-v2/68190): > > Automation Professionals is pleased to announce its latest EtherNet/IP Communications Suite driver module, a major upgrade to its EtherNet/IP Class1 Communications module, as a Public Beta. As of April 15, 2023, this is now a Production Release. The primary new feature is its new Generic EtherNet/IP Client Driver, a drop-in replacement for IA's Logix V21+ driver and its Omron NJ/NX driver. It does work with older Logix processors, and also works with Rockwell's MicroLogix 8xx family (ethernet…