M172 - BACnet controlling exceptions and read-only status

[obscuresc]

Hi,

I have BACnet running on an M172 with a few points. My project should handle different units (e.g. celsius v fahrenheit). Right now, I am using a global EEPROM setting that a user will set in on the HMI.

When the setting is changed - 

• I would like the BACnet 'Units' property to be read-only, using the new value. 
• I would like the acceptable range of 'Present Value' to change (e.g. a maximum of 30degC or 86degF) and reporting an Exception over BACnet if this is violated.

How can I go about this?

This is for the TM172PDG18R, ESME HVAC v1.10

Cheers!

[FedericoM]

Hello,

units is a RW properties that you can change from IEC code, the only way to make it "Read Only" is don't store it into EEprom and write it continously.

About the range you can play with High and Low Limit, Limit Enable and Event Enable, but not that these are settings which are normally configured from BMS side.

If you force them from IEC code, you are not fully aligned with BACnet specification, you have to mention in the documentation that these settings can't be modified.

[obscuresc]

Hi @FedericoM,

Is this something that could be updated? I'd prefer returning a BACnet Exception if the user sets a value that is out of range etc, rather than overwriting.

Thanks.

[FedericoM · Accepted solution]

The out of range is generated if the written value is out of range with respect to BACnet specification (Min_Pres_Value and Max_Pres_Value are optional fields not supported). It's not planned to add these optional properties, we have just completed the BTL re-certification

You can't have a read only value if the BACnet specs define it as RW.