Hello everyone,
I’m experiencing a strange issue when using the Vago CC100 as a Modbus RTU master, and I’d like to understand if this is related to timing, frame handling, or internal buffering.
Scenario
CC100 acting as Modbus RTU master with Multiple slaves (currently 7) throught RS-485, 2-wire,
polling cyclically (same request sequence every cycle) each 1 second.
Baud rate (9600) and parameters are correct and stable.
The first slave in the sequence fails with what appears to be a broken or incomplete Modbus frame
Frame starting mid-byte or truncated. Then, on the next cycle, the error shifts to the next slave, and so on — as if the bus or driver state is not being fully reset between cycles.
Observations
No electrical noise (short cables, proper termination)
Looks like the CC100 may be not respecting the Modbus RTU silent maximum interval (3.5 chars), or reusing an internal buffer before the line is fully idle.
I’m using CODESYS (Devices configuration and I/O Mapping) on a CC100 as a Modbus RTU master. The driver is edge-triggered (FALSE → TRUE) by the application, and I’m using Modbus Channels for the transactions.
Questions
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Does the CC100 internally guarantee the 3.5 character silent time between frames?
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Is there a known issue with back-to-back Modbus RTU requests?
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Are there any known limitations or caveats when polling multiple Modbus slaves sequentially?
Additional Info
If I slow down the polling rate or insert an artificial delay between cycles, the issue does not go away, which makes me suspect a timing or buffer-release problem inside the CC100.
See below time sequence. There is a GAP inside the frame about 8.77 ms.
Any insight or best practices for reliable Modbus RTU operation with the CC100 would be greatly appreciated.
Thanks in advance!
