On the back side of Slave module there are three terminals for RS485, in manual, mentioned A,B,SCR, Could you please describe which one is (+) and (-) because I am not able to find the polarity in technical manual.

A_

Actually there is no defined standard for - / + of an RS485 system. This is why DSE uses A and B. You will find that MOST other manufacturers of RS485 equipment design their systems so that A of DSE is - (minus) of the other device and DSE B = other +

However the other systems don't always follow this rule, Try first A to minus, B to plus. If this doesn't work, simply swap over A and B.

Dear Kaulquappe,

In third party slave device manual, there is mentioned.

“ The byte format over an RS485 link shall be 1 start bit, 8 data bits, no parity bit and 2 stop bits as defined by the Modbus protocol”

With this setting in Modbus poll, the reading writing was successful, but not in Siemens Modbus master system.

I have changed configuration with 1 stop bit no parity bit in module hardware configuration then able to read the value., RS485 polarity and Stop bit both are confusing and against the manual.

and you know in Siemens manual at page 167 mentioned, If you set the parity to "none", you must select 2 stop bits.

Now we are using fuction code 3 and bit count 70 the readings are correct in RCV destination DB with INT formate and both LED's flashing on 2Hz.

But we wish to read the first 500 registers when we change and write the bit count 70 to 100 both LED's flashing on 4Hz. and nothing to receive in DB.

and as well we need to Read/Write multiple registers but modbus master not responding with function code 16.

could you please describe when we connect the multiple slave devices with modbus master how can we write the Slave address in DB42.DBB0 because there is mentioned in manual at page 133.

"In 2-wire operation it is possible to connect as many as 32 slaves to one master in half-duplex operation"

Regard's