–
Cmd = 3…7: Reserved Cmd values
●
Priority: to write or relinquish the BA priority slot (for BA output objects and
process value objects only)
–
Represents BA present priority (1…17) in case of Modbus read response
–
Contains the priority of the priority slot to be written or relinquished in case
of Modbus write request, only prio 1, 8, 13 can be written.
NOTICE! Operators need to be aware of the risk of override physical
outputs by prio1.
–
Priority field is void for BA object types without priority array support.
●
Modbus write request: Allowed combinations of Cmd and Priority
–
for BA output objects and process value objects:
Cmd
Priority
Description
0: ready, or
>2: reserved values
Don't care
Not allowed, to be discarded by the server
1: command new value
1...16
To write the BA priority slot according to the priority field
0 or >16
Not allowed, to be discarded by the server
2: relinquish
1..16
To relinquish the priority slot according to the priority field
0 or >16
Not allowed, to be discarded by the server
–
for BA object types without priority array support, e.g. Config (Ref) value
object:
Cmd
Priority
Description
0: Ready, or
>2: reserved values
Don't care
Not allowed, to be discarded by the server
1: Command new value
Don't care (0)
To write BA present value.
Priority field is ignored by the server.
We recommend that the client sets the priority field to zero
in the request message
2: Relinquish
Don't care
Not allowed, to be discarded by the server
●
Modbus read response: Allowed combinations of Cmd and Priority
–
for BA output objects and process value objects:
Cmd
Priority
Description
0: Ready
1..17
Field Cmd is reset to ‘ready’ by the Modbus Slave BA Adapter after the
write command is executed.
Field Priority represents property present priority
other values
Don't care
Not allowed
–
for BA object types without priority array support, e.g. Config Ref value
object:
Cmd
Priority
Description
0: Ready
Don't care
(0)
Field Cmd is reset to ‘ready’ by the Modbus Slave BA Adapter after the
write command is executed
Field Priority is void. We recommend that the server sets the priority field
to zero in the response message
other values
Don't care
Not allowed
–
Reliability:
- 16 bit enumeration with BACnet reliability encoding for a Modbus read
response.
- Void field (0) for a Modbus write request: To be ignored by the 'Modbus
Slave BA Adapter'.
–
Reserved fields r(0) are set to zero by the sender and ignored by the
receiver.
Engineering of communicative devices
Modbus slave
6
164 | 170
A6V10733786_en_c
