TPU2000/2000R Modbus/Modbus Plus Automation Guide
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If a node had to cross a network boundary through a Bridge, the examples illustrate how node access addressing
would be affected.
Modbus and Modbus Plus General Notes
Modbus is an exceptional protocol for bridging a majority of vendor devices to communicate to each other. The
generation of each protocol, throughput, robust capabilities and troubleshooting techniques shall be covered in
later sections. The understanding of each of these principles shall aid the implement in exploiting the capabilities
within their own automation system.
Modbus ASCII, Modbus RTU, and Modbus Plus have the following capacities implemented within the TPU2000
and TPU2000R.
 01 - Read 0X Coil Status
 02 - Read 1X Contact Status
 03 - Read 4X Holding Registers
 16 - Write 4X Holding Registers
 08 - Diagnostics
 23 - Write 4X and Read 4X Holding Registers
 20 - Read 6X Extended Registers
 21 - Write 6X Extended Registers
The TPU2000 and TPU2000R emulates a slave device. Any other Modbus command sent to the TPU2000 and
TPU2000R shall result in a Modbus exception code being sent to the transmitting device. The following sections
will further describe the Modbus functionality within the TPU2000 and TPU2000R.
IMPLEMENTATION TIP-Although the TPU2000 and TPU2000R allows configuration of Modbus for a Frame of N-
8-1, some implementations will interpret this emulation of Modbus to be RTU Mode. The TPU2000 and
TPU2000R does not support this mode. It is advisable to contact the manufacturer of the host and host software
to determine the interpretation of the command string. For example, the Modicon XMIT and COMM BLOCK
allowing the PLC to emulate a host device only allows block frame size designation of 7 data bits.
Modbus/Modbus Plus Register Map
0X Discrete Coils
Discrete Modbus Coil status is available via a function 01 request via Modbus. Figure 5-14 illustrates a typical
command sequence. The Host polls the TPU2000/TPU2000R for the Data. The TPU2000/2000R receives the
request and responds with the expected data. The Host then interprets the command response, checks the
checksum (LRC if ASCII, CRC 16 if RTU mode and then displays the interpreted data. Additional information is
available in Modicon’s protocol manual references listed at the beginning of this document.
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