144 SI-Ethernet User Guide
Issue: 3
7.2.11 Modbus Exception Response Message
If the master request is rejected then an exception response message will be returned.
Exception Response Message
The master request function code will be returned but with bit b7 set (e.g. function code 0x03 will
be returned as 0x83)
7.3 RTMoE (Real Time Motion over Ethernet)
This is a communication protocol developed to support the functionality previously offered by
CTNet and CTSync.
RTMoE provides:
• Drive synchronization using the Precision Time Protocol (PTP) otherwise known as
IEEE1588 V2
Each PTP device has a tuneable clock running. Following an arbitration process the
devices select a master and tune their clocks until they are synchronized to that master.
This process may take several seconds to complete.
• Data transfer
• Cyclic data (synchronous and non-synchronous) is sent using the User
Datagram Protocol (UDP)
• Non-cyclic data is sent using the Transmission Control Protocol (TCP)
• Cycle time down to 500 µs
• Jitter less than 1 µs
RTMoE can be configured in two ways:
• Via Machine Control Studio using the cyclic link editor or
• Via parameters using the Easy Mode menus (10 and 11)
The full capabilities of RTMoE are available only when using Machine Control Studio.
Table 7-6shows the comparison between Easy Mode and Machine Control Studio support levels.
Byte Hex value Description
0-1 ?? ?? Transaction ID (defined by Modbus Master)
2-3 00 00 Protocol ID
4-5 00 03 Number of data bytes to follow
6 ?? Unit identifier
7 ?? Function code (request FC with bit b7 set to 1)
8??
Exception code
01 = Function code not supported
02 = Invalid register address
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