# Address configuration for s7 1200 + Modbus TCP **URL:** \ **Category:** Ignition\ **Tags:** designer\ **Created:** [October 11, 2025, 11:35am UTC](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-modbus-tcp/111360 "2025-10-11T11:35:32Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![rsrigokul](https://avatars.discourse-cdn.com/v4/letter/r/f1d935/32.png) [@rsrigokul](https://forum.inductiveautomation.com/u/rsrigokul)\ **Post date:** [October 11, 2025, 11:35am UTC](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-modbus-tcp/111360/1 "2025-10-11T11:35:32Z")
error writing to value.value: Bad\_GatewayCommOff how to solve this issue for HR8.1 write ---
**Author:** ![David\_Stone](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/david_stone/32/79749_2.png) [@David\_Stone](https://forum.inductiveautomation.com/u/David_Stone)\ **Post date:** [October 11, 2025, 12:27pm UTC](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-modbus-tcp/111360/2 "2025-10-11T12:27:32Z")
> **[About Communication Modes Video at Inductive University](https://inductiveuniversity.com/videos/about-communication-modes/8.3)** > > Learn how to change the Designer's communication mode: Comm Off, Comm Read-Only, and Comm Read/Write. The default setting does not allow writing from the Designer to Tag or database sources. ---
**Author:** ![rsrigokul](https://avatars.discourse-cdn.com/v4/letter/r/f1d935/32.png) [@rsrigokul](https://forum.inductiveautomation.com/u/rsrigokul)\ **Post date:** [October 13, 2025, 6:08am UTC](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-modbus-tcp/111360/3 "2025-10-13T06:08:36Z")
i did the changes as mentioned in the video but still same issue ---
**Author:** ![David\_Stone](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/david_stone/32/79749_2.png) [@David\_Stone](https://forum.inductiveautomation.com/u/David_Stone)\ **Post date:** [October 13, 2025, 6:12am UTC](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-modbus-tcp/111360/4 "2025-10-13T06:12:18Z")
> [@rsrigokul](#): > > Bad\_GatewayCommOff This indicates that you are in read-only mode in the designer. ---
**Author:** ![rsrigokul](https://avatars.discourse-cdn.com/v4/letter/r/f1d935/32.png) [@rsrigokul](https://forum.inductiveautomation.com/u/rsrigokul)\ **Post date:** [October 13, 2025, 6:17am UTC](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-modbus-tcp/111360/5 "2025-10-13T06:17:18Z")
i changed to read/write in the designer. can you please provide the steps if any to cross verify ? ---
**Author:** ![David\_Stone](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/david_stone/32/79749_2.png) [@David\_Stone](https://forum.inductiveautomation.com/u/David_Stone)\ **Post date:** [October 13, 2025, 6:18am UTC](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-modbus-tcp/111360/6 "2025-10-13T06:18:18Z")
What does the message say now? Perhaps show a screenshot? ---
**Author:** ![rsrigokul](https://avatars.discourse-cdn.com/v4/letter/r/f1d935/32.png) [@rsrigokul](https://forum.inductiveautomation.com/u/rsrigokul)\ **Post date:** [October 13, 2025, 7:18am UTC](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-modbus-tcp/111360/7 "2025-10-13T07:18:34Z")
> [@rsrigokul](#): > > writing to value.value: Bad\_GatewayCommOff Error writing to value.value: Bad ---
**Author:** ![David\_Stone](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/david_stone/32/79749_2.png) [@David\_Stone](https://forum.inductiveautomation.com/u/David_Stone)\ **Post date:** [October 13, 2025, 7:33am UTC](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-modbus-tcp/111360/8 "2025-10-13T07:33:11Z")
> [@rsrigokul](#): > > HR8.1 Show us how you have set up your tag. This above is incorrect. Consider the below OPC Address: `ns=1,s=[device]1.HR8` this would get you the whole word, you cannot get one bit out of a holding register unless you have a specific type of modbus device. Either use the Siemens Driver with your S7-1200, or read up on how to use the Modbus driver. > **[Modbus Addressing | Ignition User Manual](https://www.docs.inductiveautomation.com/docs/8.1/ignition-modules/opc-ua/opc-ua-drivers/modbus/modbus-addressing)** > > Manually Addressing a Modbus Device ---
**Author:** ![rsrigokul](https://avatars.discourse-cdn.com/v4/letter/r/f1d935/32.png) [@rsrigokul](https://forum.inductiveautomation.com/u/rsrigokul)\ **Post date:** [October 13, 2025, 7:45am UTC](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-modbus-tcp/111360/9 "2025-10-13T07:45:47Z")
[MB]HR8.0 this was the OPC address in this same format i am able to read the bool data but write bool date to PLC throwing the above error ---
**Author:** ![David\_Stone](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/david_stone/32/79749_2.png) [@David\_Stone](https://forum.inductiveautomation.com/u/David_Stone)\ **Post date:** [October 13, 2025, 7:52am UTC](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-modbus-tcp/111360/10 "2025-10-13T07:52:16Z")
> [@Address configuration for s7 1200 as OPC device](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-as-opc-device/96583/24): > > Based on your earlier error report, the Modbus implementation in Siemens doesn't support the necessary "Masked Write" function code to change bits in holding registers, and doesn't support the coil function codes. So, no can do with Modbus. It should be possible with the native driver using boolean tag syntax as Kevin suggested in [comment #17 above](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-as-opc-device/96583/17), as long as you satisfy all of the preconditions for the native driver's use with S7 1200/1500 devices: (An S7+ driver is coming in Ignition v8… Siemens does not support writing to the Holding Registers in this way. I suggest you use the Siemens driver instead. ---
**Author:** ![rsrigokul](https://avatars.discourse-cdn.com/v4/letter/r/f1d935/32.png) [@rsrigokul](https://forum.inductiveautomation.com/u/rsrigokul)\ **Post date:** [October 13, 2025, 7:58am UTC](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-modbus-tcp/111360/11 "2025-10-13T07:58:42Z")
I understand but I wanted to use Mobbus TCP for Modbus TCP simulation attack. is any other way to write bool tag in S71200? ---
**Author:** ![David\_Stone](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/david_stone/32/79749_2.png) [@David\_Stone](https://forum.inductiveautomation.com/u/David_Stone)\ **Post date:** [October 13, 2025, 8:02am UTC](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-modbus-tcp/111360/12 "2025-10-13T08:02:28Z")
Use Coils (Modbus calls Booleans Coils thanks to a bunch of history) ---
**Author:** ![rsrigokul](https://avatars.discourse-cdn.com/v4/letter/r/f1d935/32.png) [@rsrigokul](https://forum.inductiveautomation.com/u/rsrigokul)\ **Post date:** [October 13, 2025, 8:39am UTC](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-modbus-tcp/111360/13 "2025-10-13T08:39:36Z")
> [@Address configuration for s7 1200 as OPC device](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-as-opc-device/96583/24): > > Based on your earlier error report, the Modbus implementation in Siemens doesn't support the necessary "Masked Write" function code to change bits in holding registers, and doesn't support the coil function codes. So, no can do with Modbus it meant both coil and HR cannot be use for writing ? ---
**Author:** ![David\_Stone](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/david_stone/32/79749_2.png) [@David\_Stone](https://forum.inductiveautomation.com/u/David_Stone)\ **Post date:** [October 13, 2025, 8:48am UTC](https://forum.inductiveautomation.com/t/address-configuration-for-s7-1200-modbus-tcp/111360/14 "2025-10-13T08:48:12Z")
I believe you are right. > [@rsrigokul](#): > > Modbus TCP simulation attack. I don't understand what you mean by this? Modbus is not native for talking to this PLC, why not use a normal method?