ABB TPU2000 Technical Manual page 364

TPU2000/2000R Modbus/Modbus Plus/ Modbus TCP/IP Automation Guide
Within the PLC, a Master Instruction should be programmed within the unit which when scanned and executed,
the PLC will transmit/receive data over the Modbus Plus Network. It may take more than one PLC scan to obtain
the data over the network. The PLC scan is never stopped to wait for the data. The PLC will continue with its
logic execution and upon a new ladder logic scan, a determination will be made by the instruction as to whether it
received the information in the appropriate amount of time. The throughput of the data acquisition is determined
by a variety of factors:
•
Ladder Logic Execution Speed.
•
Token Rotation Speed of Modbus Plus.
•
Amount of data travelling over the network at the time of the request.
•
Latency of the receiving device to respond to the request when received.
The MSTR (Master) Block is illustrated in Figure 4. A single PLC may have up to four Master Blocks active at any
one time accessing data from the ABB protective relay. The amount of data, which may be requested by a PLC,
is determined by the amount of free data paths available on the PLC. The ABB protective relay has up to 8 data
paths, which may be accessed and busy at one time. The MSTR instruction block is parameterized via the PLC's
Ladder Logic to perform the intended functions as illustrated via the function codes. If one was to obtain data
from the GLOBAL data path, the amount of active MSTR instructions could be in a number greater than four.
The MSTR instruction is executed whenever the ENABLE instruction leg is energized. If the instruction is
enabled, the ACTIVE output at the right side of the instruction shall energize. When the instruction has executed
correctly, the COMPLETE instruction leg shall energize and the ACTIVE leg shall de-energize. If an error occurs
within parameterization or timeout of the network without a response, the ERROR leg shall energize and the
ACTIVE leg shall de-energize. The parameterization shall occur through configuration of the correct 4XXXX
registers via the table provided for the instruction. If an error occurs, register 4XXXX +1 shall contain a number
other than 0 indicating the failure. If a successful communication occurs, the data will be transferred into register
block 4YYYY to 4YYYY + NNN (if a read operation or network statistics read operation) or data transferred from
the PLC block 4YYY to 4YYYY + NNN if the MSTR operation is a write.
Enable
Abort
Meter Data Access To a PLC Host From an ABB Relay
Figure 5 illustrates a typical installation in which a PLC is to access data from an ABB DPU2000R using a Master
Instruction.
4 XXXX 4XXXX
Active
4XXXX +1 = Block Error Status
4 YYYY 4XXXX +2 = Length of Data
4XXXX +3 = Operation Dependent Data
Error
MSTR 4XXXX +4 = Routing Address 1
4XXXX +5 = Routing Address 2
4XXXX +6 = Routing Address 3
NNN
Complete
4XXXX +7 = Routing Address 4
4XXXX +8 = Routing Address 5
4YYYY
4YYYY +1
4YYYY +2
4YYYY + NNN
Figure 4. Modbus Plus Master Instruction
= Operation Type
Operation Types
1 = Write Data
2 = Read Data
3 = Get Local Statistics
4 = Clear Local Statistics
5 = Read Global Data
6 = Get Remote Statistics
7 = Clear Remote Statistics
354