# Derived tag, multiple bit to modbus tag **URL:** \ **Category:** Ignition\ **Created:** [May 19, 2020, 7:19am UTC](https://forum.inductiveautomation.com/t/derived-tag-multiple-bit-to-modbus-tag/34871 "2020-05-19T07:19:37Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![SBL\_MC](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/sbl_mc/32/56813_2.png) [@SBL\_MC](https://forum.inductiveautomation.com/u/SBL_MC)\ **Post date:** [May 19, 2020, 7:19am UTC](https://forum.inductiveautomation.com/t/derived-tag-multiple-bit-to-modbus-tag/34871/1 "2020-05-19T07:19:37Z")
Hi all, Need some advice on how to solve this. We use derived tags to set and reset bits in a modbus int, command word. This works as long as we do bit by bit. But… I got some buttons that is intended to alter 3 bits at once. It seems that we run into some timing issues, as only the last instruction is done. I have tried both system.tag.write and system.tag.writeAll on my 3 derived tags. Button 1 Set bit 10 Res bit 11 Res bit 12 Button 2 Res bit 10 Set bit 11 Res bit 12 Button 3 Res bit 10 Res bit 11 Set bit 12 Example derived tag: Read expression: getBit(toInt({source}),12) Write expression: if({value}, toInt({source}) | (1 \<\< 12), toInt({source}) & ~(1 \<\< 12)) IGN 8.0.9 Thanks in advance. ---
**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:** [May 19, 2020, 12:55pm UTC](https://forum.inductiveautomation.com/t/derived-tag-multiple-bit-to-modbus-tag/34871/2 "2020-05-19T12:55:33Z")
Enable the “Optimistic Writes” option for the tag group these tags belong to. ---
**Author:** ![SBL\_MC](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/sbl_mc/32/56813_2.png) [@SBL\_MC](https://forum.inductiveautomation.com/u/SBL_MC)\ **Post date:** [May 19, 2020, 1:15pm UTC](https://forum.inductiveautomation.com/t/derived-tag-multiple-bit-to-modbus-tag/34871/3 "2020-05-19T13:15:59Z")
Hi Kevin, We tried this with no luck. ---
**Author:** ![SBL\_MC](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/sbl_mc/32/56813_2.png) [@SBL\_MC](https://forum.inductiveautomation.com/u/SBL_MC)\ **Post date:** [May 25, 2020, 10:45am UTC](https://forum.inductiveautomation.com/t/derived-tag-multiple-bit-to-modbus-tag/34871/4 "2020-05-25T10:45:40Z")
Hi Kevin, Restored the gateway on our test server and connected to a PLC on my desk. Enabling optimistic write does nothing, first when we change optimistic write timeout from 0 to 3000 we see a difference. It works better, meaning two or more bit is not high at the same time - but the first press will most times only disable bits. It will require a second or more click to enable the bit we would like to set. 3 buttons, 3 bits that needs to be altered. All of them belong in a UDT. Tried to add derived tags without a UDT but still the same. Script, event: > system.tag.write("[TKV\_TagProvider]D52\_HFS\_Kjoling/HFS/OBJ/Kommando/Pri P2",False) > system.tag.write("[TKV\_TagProvider]D52\_HFS\_Kjoling/HFS/OBJ/Kommando/Pri Alt",False) > system.tag.write("[TKV\_TagProvider]D52\_HFS\_Kjoling/HFS/OBJ/Kommando/Pri P1",True) ---
**Author:** ![SBL\_MC](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/sbl_mc/32/56813_2.png) [@SBL\_MC](https://forum.inductiveautomation.com/u/SBL_MC)\ **Post date:** [May 25, 2020, 10:50am UTC](https://forum.inductiveautomation.com/t/derived-tag-multiple-bit-to-modbus-tag/34871/5 "2020-05-25T10:50:14Z")
Also tried writeAll, still the same. ---
**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:** [May 25, 2020, 12:57pm UTC](https://forum.inductiveautomation.com/t/derived-tag-multiple-bit-to-modbus-tag/34871/6 "2020-05-25T12:57:26Z")
It works for me when using writeBlocking: ```auto tags = [ "[default]IntBits_Instance/Bit0", "[default]IntBits_Instance/Bit1", "[default]IntBits_Instance/Bit2", "[default]IntBits_Instance/Bit3" ] values = [1,1,1,1] system.tag.writeBlocking(tags, values) ``` or ```auto system.tag.writeBlocking(["[default]IntBits_Instance/Bit0"], [1]) system.tag.writeBlocking(["[default]IntBits_Instance/Bit1"], [1]) system.tag.writeBlocking(["[default]IntBits_Instance/Bit2"], [1]) system.tag.writeBlocking(["[default]IntBits_Instance/Bit3"], [1]) ``` It didn’t work with individual async writes, though, and I’m not sure if that’s correct behavior or not. I’ll have to open a ticket and get someone to look into it this week. ---
**Author:** ![SBL\_MC](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/sbl_mc/32/56813_2.png) [@SBL\_MC](https://forum.inductiveautomation.com/u/SBL_MC)\ **Post date:** [May 25, 2020, 1:50pm UTC](https://forum.inductiveautomation.com/t/derived-tag-multiple-bit-to-modbus-tag/34871/7 "2020-05-25T13:50:14Z")
Hi Kevin, thanks for writing back. I tried using writeBlocking now. Its maybe a bit improved. I had to swap about 8-9 times before it failed again. My command word is set to zero. Looking forward to what the ticket brings. Have a nice day. ---
**Author:** ![SBL\_MC](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/sbl_mc/32/56813_2.png) [@SBL\_MC](https://forum.inductiveautomation.com/u/SBL_MC)\ **Post date:** [June 4, 2020, 10:32am UTC](https://forum.inductiveautomation.com/t/derived-tag-multiple-bit-to-modbus-tag/34871/8 "2020-06-04T10:32:12Z")
Hi Kevin, Do you have any news for us? 🙂 ---
**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:** [June 4, 2020, 2:54pm UTC](https://forum.inductiveautomation.com/t/derived-tag-multiple-bit-to-modbus-tag/34871/9 "2020-06-04T14:54:42Z")
Sorry, this fell off my radar. I just wrote up a ticket so it won’t get forgotten.