Varec TankGate Interface 8315 Series - Manual (Page 35)

8315 TGI Software Description
Varec, Inc. 25
The Modbus Slave protocol handler is flexible, allowing the user to set options for handling
several aspects of Modbus communications. The Modbus Slave uses the GWBLK Gateway Block
as a lookup table for data addresses.
The Gateway Block allows the user to specify data address and point reference combinations.
This allows the Tank Gate Interface to be used with an existing system that is already configured.
The user defines a GWBLK point and specifies which parameter in the Tank Gate Interface will
be used for a particular address. When a request from a master is received, the Modbus Slave
protocol handler will first search for any GWBLK points and determine if the data address of the
request is specified in one of the GWBLK points. If the data address is contained in a GWBLK
point, then the corresponding point reference is used to provide the data for the reply to the
master.
COM 0 will automatically sense whether the host system is ViewRTU or a Modbus Master. The
communications parameters for COM 0 are 9600 baud, 8 data bits and No Parity. When
switching between ViewRTU and Modbus communications, it is necessary to wait 60 seconds for
the current protocol to time-out. The Tank Gate Interface will go back to the auto sensing mode
and wait for a request. When a request is received, the Tank Gate Interface will determine if the
request is from ViewRTU or a Modbus Master. If the Tank Gate Interface has problems switching,
press the Reset button and this will force the Tank Gate Interface back into the auto sensing
mode.
Note COM 1 (if available) is always a Modbus Slave. The communications parameters for
COM 1 are 9600 baud, 8 data bits and No Parity. COM1 is not available on the 8315 Tank
Gate Interface
Note The Tank Gate Interface uses the ID switch in determining to which address on the
communications bus to respond.
Tank Gate Interface responds to the following Function Codes:
There are two methods for data addressing within the Tank Gate Interface
•
The Tank Gate Interface has a fixed Modbus Map of selected parameters
•
Gateway Block (GWBLK) software blocks can be configured to set the data address
Function Code Description Comments
3 Read Output
Register
FC 3 and FC 4 are treated the same. Use either FC 3 or FC 4 to read
data from the Tank Gate Interface
4 Read Input
Register
5 Force Single
Output Status
FC 4 and FC 6 are treated the same. Use either FC 5 or FC 6 to write
data to the Tank Gate Interface
6 Preset Single
Register
15 Force Multiple
Outputs
FC 15 and FC 16 are treated the same. Use either FC 15 or FC 16 to
write multiple registers to the Tank Gate Interface
16 Preset Multiple
Registers