ProSoft Technology PS-QS-1x10-0781 - Manual (Page 54)

FieldServer Configuration Manual Page 54 of 90
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8.5 Handling of Successive Writes to the Same Point
When multiple successive port expansion writes to the same point occur, there is a potential build-up of pending
write transactions in the FieldServer, since the Server side may receive write transactions at a faster speed than
they are completed on the Client side (depending on the speeds of the respective protocols).
There are two fundamental ways of dealing with the potential accumulation of successive writes to the same
point:

Overwrite – any pending write values that have not yet been sent to the Server are overwritten with the
latest write value. This is the default option and it ensures that the last value that was received from the
Client is written to the Server. Intervening writes may be lost.

Blocking – if it is important to preserve the sequence of write values to the same point (e.g. a switching
sequence of on/off transitions), then the Server can be configured to handle writes in a blocking mode.
Here successive writes to the same point are queued to a configurable maximum length. Writes are
accepted from the Client until the queue is full, at which point further writes will be rejected. This option
must be configured on the Server using the following Connection parameters and values:
Column Title Function Legal Values
Write_Queue_Mode
Mode for dealing with potential accumulation of successive writes to
the same point can be configured. Overwrite,
Blocking.
Write_Queue_Size
The length of the queue can be configured if blocking mode is set.
Blocking will occur when there is no more space on the Write_Queue.
If size=0 every successive write is blocked. A message will be displayed
when blocking occurs, except if the Queue_Size=0.
Non-negative
integer, 0
Connections
Port , Baud , Parity , Data_Bits , Stop_Bits , Protocol
, Handshaking , Poll_Delay , Write_Queue_Mode , Write_Queue_Size , Timeout
P1 , 9600 , None , 8 , 1 , Modbus_RTU , None , 0.100s , Blocking , 5 , 8s
8.6 Port Expansion Configuration:
The example configuration file for this mode is available from FieldServer Technical Support if needed. Although
Map Descriptor configuration is not required, Connections and Nodes do need to be configured.
Connection
Port , Protocol , Server_Hold_Timeout
P1 , mb_rtu , 12
P2 , mb_rtu , -
Nodes
Node_Name , Node_ID , Protocol , Port , Timeout , Write_Ack_Option
Dev1
, 1 , mb_rtu , P2 , 12 , Ack_Immediate