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5 Modbus TCP Slave
5.1 Working Principle
Data exchange of Modbus TCP and PROFIBUS DP of EP-321MP is set up through “mapping”. There are
two data buffer areas, one is PROFIBUS DP network input buffer and the other is PROFIBUS DP network output
buffer. Network input and output buffer is all for PROFIBUS DP. When the gateway acts as Modbus TCP slave,
Modbus write register command will write the read data to the network input buffer for PROFIBUS DP accessing.
Modbus read command gets data from network output buffer and export to the Modbus TCP master equipment
through response message.
The gateway acts as Modbus TCP slave, support function: 03H, 04H, 06H and 10H. Users can select 03H
function code to read the data PROFIBUS DP master outputted or use 04H function code to read he data
PROFIBUS DP master outputted.
Network input buffer is Modbus TCP master output at the Modbus TCP side. It is mapped to the Modbus
holding register. Users can use No.3 command or No.4 command to read back. Users can select command No.
in the configuration software.
Network output buffer is Modbus TCP master input. It is mapped to Modbus input register. Users can use
No.4 or No.3 function code to read data. Users can select command No. in the configuration software.
5.2 Network Status Monitoring
When the Gateway is a Modbus TCP slave, the gateway has the function of monitoring the network status.
When the Monitoring is enabled, the first word of input buffer is used as counter which record the number of
TCP connections.
PROFIBUS
Input buffer
PROFIBUS
Output buffer
… …
0004H
0001H
0000H
0002H
0003H
0005H
0004H
0001H
0002H
0000H
0003H
0005H
… …
Modbus
Write
command 06,10H
Modbus
Read command
03H or 04H
Modbus
Read command
03H or 04H
Modbus
Read command
03H or 04H
Summary of Contents for EP-321MP
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