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# #ccsd-water-ignition — 2025-12-19
**06:02 [Mason Radke](https://slack.com/archives/C08TVA84PD4/p1766152960870049):** i got the modbus write messages to work. so the PLC can now toggle DO's on the optos.
**06:03 [Mason Radke](https://slack.com/archives/C08TVA84PD4/p1766152991687709):** im assuming a well call or pump run will be sent to the optos? in this example of the SSWF w2?
**06:03 [Mason Radke](https://slack.com/archives/C08TVA84PD4/p1766153024108469):** i also did some research on the prosoft.. the way i have it setup serializes the messages.. it processes one at a time and moves onto the next on a success, fail, or timeout
**07:42 [Mason Radke](https://slack.com/archives/C08TVA84PD4/p1766158959425329):** @andy is there/could there be an existing system writing to the DOs on these optos? i can set the DO status, but it seems to be flickering between 0 and 1.. wondering if my writes are competing with another system possibly? maybe there is logic writing to these points? i set up DO/2 which was not being used for anything previously.. but maybe soething is writing to the block of DOs? trying to make sense of it
**07:50 [Mason Radke](https://slack.com/archives/C08TVA84PD4/p1766159435226129):** actually i think its a prosoft configuration.
**08:31 [Kevin](https://slack.com/archives/C08TVA84PD4/p1766161860223399):** You are being careful to not cause issues writing DOs ?
**08:41 [Mason Radke](https://slack.com/archives/C08TVA84PD4/p1766162481095279):** writig to Unused DOs
**09:14 [andy](https://slack.com/archives/C08TVA84PD4/p1766164467556039):** This is a live SCADA system, there is an Opto 22 controller running the system now.
It’s possible the way Opto handles unused IO is writing zeroes to it?
Opto discrete IO requires no config so we could pop an output or input card at the end of a rack and let you test on it.
**09:14 [Mason Radke](https://slack.com/archives/C08TVA84PD4/p1766164497455029):** that might be helpful
**09:16 [andy](https://slack.com/archives/C08TVA84PD4/p1766164568020969):** Each RTU has its own PLC and opto program. I have all of those backed up so you can open them and see which IO os being referenced and where