Appendix B - Data Exchange Interface
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Appendix B - Data Exchange Interface
The Data Exchange Interface is a bi-directional interface
that enables both transmitting and receiving data
between the Therm-O-Flow system and the controlling
logic (PLC). The interface allows a large amount of data
to exchange between the systems while only occupying
a very small data map to support the exchange. The
interface also allows for future expansion of data without
changing the map structure.
To get or receive data from the supply system
, the con-
trolling PLC needs to:
1. Write to the Data Exchange Interface Pointer Output
Designation location on the map (output instance 6)
a value corresponding to the data the PLC wants to
receive.
2. Wait for the Therm-O-Flow to provide the same
Pointer Designation number written in the previous
step at input instance 67 (Data Exchange Interface
Pointer Last Serviced).
3. Read the requested data at input instance 68, Data
Exchange Interface Input Value.
To write or transmit data to the supply system
, the con-
trolling PLC needs to:
1. Write the data for the Therm-O-Flow system to the
Data Exchange Interface Output Value location, out-
put instance 7.
2. Write to the Data Exchange Interface Pointer Output
Designation location on the map (output instance 6)
a value corresponding to the data the PLC is going
to transmit to the supply system.
3. The Therm-O-Flow system echoes back to the PLC
the Pointer Designation and the Data Interface
Value after the Therm-O-Flow system processes
the data transmit request to input instances 67 and
68 respectively.
When the controlling logic is exchanging data over this
interface, the Therm-O-Flow system sets the Data
Exchange Interface Active or in Transition status bit
while it processes the request and writes to the Data
Exchange Interface input locations (input instances 67
and 68).
After valid data is present at the input instances, the
Therm-O-Flow system clears the bit. While the bit is set,
the controlling PLC should ignore the interface inputs
until the bit is cleared. After the Therm-O-Flow system
services the request, the designation pointer input
matches the designation pointer output. If the scan rate
of the controlling PLC or control logic is slow enough,
monitoring of the status bit may not be necessary.
NOTE:
When changes are made over the Data
Exchange Interface, the Therm-O-Flow system display
screen may not update immediately. It may be neces-
sary to navigate away from the screen, then back to it.
