The destination of data for an Analog Output object will be writing the remote Modbus register via the map indicated by the Device Link. The Modbus device will be updated upon change of source data and/or periodically as defined by the Write Map.

The Analog Output object is commandable, meaning the BACnet client must write both a value and a priority level for that value. The highest level value will be the one written to the Modbus register. If all values are relinquished, the relinquish default value will be written to the Modbus register.

To set an output object manually from this page, check the Force box, enter a value in the Present Value window, and select a priority level to assign to your forced value. Then click Update. To return a given priority level to NULL, simply type the word NULL in the Present Value window, check Force, and click Update.

Out of service means the Modbus register will not be written. Values written by the BACnet client will be retained, but only applied when this object is placed back in service. At that time, the highest priority value will be written to the Modbus register.

Reliability codes may be any of the following:
Modbus client, no response (64)
Modbus client, crc error (65)
Modbus exception, illegal function code (66)
Modbus exception, illegal data address (67)
Modbus exception, illegal data value (68)
Modbus exception, code+65, rarely used (69..79)
Local device, configuration property fault (80)
Faulty Modbus packet(81)
BACnet IP client, device timeout (82)
BACnet IP client, error returned by server (83)

Status flags A,B,C,D indicate the following, 0 meaning not true, 1 meaning true:
A = in alarm
B = fault
C = overridden
D = out of service

Device link will indicate RTU or TCP, followed by R for read or W for write, and a number which is the rule number in the table of read or write rules for mapping Modbus to this BACnet object. The designation R means read from Modbus, and W means write to Modbus.