Hey guys, I have an AB Micro850 connected with a PV+ using Modbus and Kepserver Enterprise, and I thought of a potential problem that I can't seem to solve on my own
As far as I know, the Micro850 does not have any nonvolatile storage, and there's no module or anything to store the current value of a variable during a power failure. This isn't ideal, so I was thinking I could use the PV+ to accomplish this.
My thought is that whenever one of the Modbus tags is changed through the HMI, the HMI will write the value to both the original tag and an internal, retentive tag acting as a backup. Then, I can set a startup macro to write the value of the internal tags to the original Modbus tags. As far as I know, this would cause the HMI to immediately write the stored values to the Micro850 when the power turns on again. The Micro850 takes significantly less time to boot than the PV+ so there would probably be a window where the Micro850 still uses its initial values, but that shouldn't be an issue.
My first question is whether or not this is a viable strategy. I don't actually have access to the HMI right now to test this, so if anyone has done something like this before, any input would be great.
If this approach does work, I have another quick question. I can't figure out a decent way to get the PV+ to actually copy the Modbus variables to retentive, internal ones. Most of the tags are adjustable through the HMI (numeric input cursor points) and a few are read-only (but they can be adjusted through the DCS) so I need some way to actually cause the HMI to periodically copy these into memory, and for the life of me I can't figure out how to do it. Any advice here would also be appreciated.
Sorry for asking so many questions without really trying anything out myself, but as I said I don't have access to the HMI so I'm just trying to plan ahead as best I can. Thanks.
As far as I know, the Micro850 does not have any nonvolatile storage, and there's no module or anything to store the current value of a variable during a power failure. This isn't ideal, so I was thinking I could use the PV+ to accomplish this.
My thought is that whenever one of the Modbus tags is changed through the HMI, the HMI will write the value to both the original tag and an internal, retentive tag acting as a backup. Then, I can set a startup macro to write the value of the internal tags to the original Modbus tags. As far as I know, this would cause the HMI to immediately write the stored values to the Micro850 when the power turns on again. The Micro850 takes significantly less time to boot than the PV+ so there would probably be a window where the Micro850 still uses its initial values, but that shouldn't be an issue.
My first question is whether or not this is a viable strategy. I don't actually have access to the HMI right now to test this, so if anyone has done something like this before, any input would be great.
If this approach does work, I have another quick question. I can't figure out a decent way to get the PV+ to actually copy the Modbus variables to retentive, internal ones. Most of the tags are adjustable through the HMI (numeric input cursor points) and a few are read-only (but they can be adjusted through the DCS) so I need some way to actually cause the HMI to periodically copy these into memory, and for the life of me I can't figure out how to do it. Any advice here would also be appreciated.
Sorry for asking so many questions without really trying anything out myself, but as I said I don't have access to the HMI so I'm just trying to plan ahead as best I can. Thanks.
