Renu Electronics GWY-00, User Manual, Page: 21 / 105

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Block #1 maps 255 coils of Toshiba PLC starting from Y000/0 to Modbus Slave coils starting from O00001.
Block #2 maps 255 registers of Toshiba PLC starting from D0000 to Modbus Slave registers starting from
401021.
Here # Words field contains 255, so if protocol and Gateway buffer permit, Modbus Master can access 255
registers / coils in one command, but in case of Toshiba - Modbus configuration, the maximum limit is 28
registers / coils in one command.
In above example, request from Modbus Master is executed as follows:
1.
Modbus Master sends command to Gateway for setting output coil O00033 to ‘1’.
2. Gateway searches defined Blocks and checks whether this coil is mapped to any Toshiba coil.
In example 4.2, output coil 000033 is mapped to Toshiba coil Y002/0 in Block 1. Gateway accepts
this command and sets Toshiba coil Y002/0 ON.
If Master sends a command to read / write a register / coil not defined in any Block then Gateway sends
exception response to master.
Suppose the Modbus master wants to set output coil O00400 ON, then,
1.
It sends command to gateway for writing output coil 000400.
2. Gateway checks whether this coil is mapped to any Toshiba coil. But as output coil 000400 is not
mapped to any Toshiba coil in any block. Gateway rejects this command and sends an exception
response to the Modbus Master.
NOTES:
1)
If multiple registers / coils are to be read or written in one command, then all the registers /
coils have to be defined in one Block.
2) As Gateway Setup Software is common for both the Gateway Modes, titles in the Block
Definition Area, may not be appropriate when using Gateway in Master - Slave mode.
3) Maximum 255 blocks can be configured in any mode.
4) Multiple bits read / write is not supported except for Toshiba PLC. For other PLC’s single bit
can read / write at a time.
5) In Master - slave mode, If somebody mapped read only registers or coils at destination end
to any registers at source end, it’s users responsibility that these registers are not going to
be written by master.
Example 4.2 Toshiba T series - Modbus Slave
This configuration can be used to make Toshiba T series PLC function as a Modbus Slave. Configure Gate-
way ports as: PLC1 Protocol - Toshiba T Series Master PLC2 Protocol - Modbus Slave. So the device
connected on PLC1 will be a Toshiba T series PLC acting as a slave and device connected on PLC2 will be
Modbus Master.