3 Drivers MODBUS RS485 ERROR#84

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otter_plc
Posts: 1
Joined: Thu May 09, 2019 2:06 am

3 Drivers MODBUS RS485 ERROR#84

Post by otter_plc » Thu May 09, 2019 2:24 am

Hi everyone,

We got connected 3 drivers through MODBUS CONNECTION in slave. Firstly, We tested the connection between PLC S7-1200 with module RS485 CB1241 as MASTER and one driver connected as slave. That test was successful, communication OK and not problems. The issue is coming when setting up the other 2 drivers connected to this one, the red light C-ON comes on giving the error number “84” on Communication MODBUS 485 from MEXE02 software. (Please, see attached a capture from Alarm monitor in Driver 2 which it is receiving Modbus signal)


- All drivers were checked before connecting, They work OK.
- The drivers are connected as slaves into one module RS485 CB1241 (being this module a Master).
- Drivers are not set as a group of slaves. (All drivers Initial group Disabled).
- MODBUS COMUNICATION works fine up to the other 2 drivers are connected together to the connection (MASTER - SLAVE (Driver1))

The function setting followed was the next:

Driver 1 (connected from module controller PLC to CN6)
BAUD: 4
ID: 1
SW1: No.1: OFF (ADDRESS NUMBER SLAVE)
No.2: ON (MODBUS RTU MODE)
No.3 and No.4: OFF (TERMINATION RESISTOR 120 ohms)

Driver 2 (connected from CN7 Driver 1 to CN6 Driver 2)
BAUD: 4
ID: 2
SW1: No.1: OFF (ADDRESS NUMBER SLAVE)
No.2: ON (MODBUS RTU MODE)
No.3 and No.4: OFF (TERMINATION RESISTOR 120 ohms)

Driver 3 (connected from CN6 Driver 2 to CN7 Driver 3)
BAUD: 4
ID: 3
SW1: No.1: OFF(ADDRESS NUMBER SLAVE)
No.2: ON (MODBUS RTU MODE)
No.3 and No.4: ON (TERMINATION RESISTOR 120 ohms)


--------------------------------------------------------------------------------------------

Once I adjusted these settings the red light C-ERR comes on with all drivers. That is happened without any command sent from PLC.
Disconnecting the power from DRIVER 2 and DRIVER 3, Driver 1 red light comes off.
For other hand, sending commands from PLC program to the driver, they got response / movement but still on red light and quite often needs to erase the error alarm to put back working again.

Could someone give any hint of this problem? It seems strange that it is happening when all drivers are connected. I verified the wiring and RS485 signals from software and we got them but the red light stands there.

Thanks,
Attachments
connection_Example.png
connection_Example.png (69.71 KiB) Viewed 44 times
link_slaves.jpg
link_slaves.jpg (76.46 KiB) Viewed 44 times
red_lights_communication.jpg
red_lights_communication.jpg (315.12 KiB) Viewed 44 times

om_tech_support_KR
Posts: 32
Joined: Thu Jan 11, 2018 3:03 pm

Re: 3 Drivers MODBUS RS485 ERROR#84

Post by om_tech_support_KR » Thu May 09, 2019 10:53 am

Hi otter_plc,

Have you tested each cable individually or turning of power to axis 1 and 2 or 3 to test axis 2 and 3 individually?
Also when you mention you send commands and you get a response / movement is this to only one axis or when the 3 axis are turned on?

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