checksum error, Modbus RTU
WRITE_DATA: ARRAY [0..4] OF WORD;
With this configuration the PLC send the data, but in ERNO still have the checkSUm error and error 16383 "Transmission is not possible at the moment. Another instance of the Function Block is already transmitting" why,.?? this is to write I´m try also read with the FCT 3 but not read nothing,.¡¡¡ thanks for your time Vignes.... I´m student and is my first PLC and my first mdbus comunication and I have problems with this,¡¡¡
Now your COM port working Fine.
Did you read and write your slaves through MODSCAN (or any other sw)?
If yes , your Modbus register is correct. If no find your slave Modbus register.
As per your comments, Transmission is not possible at the moment. Another instance of the Function Block is already transmitting"
My suggestion is ,
1.Remove your blink block.
2.Instead of blink ,create 1 local variable.
3.Make that high ,test 1 cycle read or write.
4.check your done bit ,error bit.
In the image posted by you, I observe that the no of Stop bits in PLC COM port configuration is 2. Set this to 2 only if the Slave has been configured with Stop Bits=2. Most slaves have by default 9600 baud rate,8 Data bits, Even parity and 1 Stop bit. In the blink block set 100ms ON time and 1000ms OFF time,since slave response time out is set to 1000ms.
While experimenting with Modbus communication, I had once observed that, the Modbus master software (in my case modscan32) would be able to communicate with a slave irrespective of whether Stop bits in Modscan32 software was set to 1 or 2.
However, this will not be the case with AC500 PLC as a master, as it strictly enforces all rules of serial communication.
Try to initially assign a cycle time of 500 ms for the task which is executing the MODBUS program. The 500ms cycle time is a good starting point for tasks handling Modbus programs.Later on, you may reduce the cycle time based on your observations of any errors arising due to further reduction in the cycle time.