Preset holding registers

[Jhav]

All,

im setting up communication with a new scale head using Modbus ip. i am able to connect the plc and the scale head but am having trouble when using the Preset holding registers to send a command read the weight and the Read input registers to read the values from the scale. I'm trying to use command # 0 . from the command list and using the Register address as the start of the vectors but it is not working so I'm leaning toward it is not right. if any one could point me in the right direction i would greatly appreciate it. 

[Gabriel Franco]

To read from the scale head use RHR #3. The start address must be 259 rather than 40259.

[Jhav]

Gabriel,

I changed the start address to 259 and am using a RHR#3 , when i keep the write address as 40001 it errors out and cannot establish connection. ive changed to 1 and it does not error out but i do not get anything when i read the scale. what should my write address be? 

[Jhav]

Gabriel,

i found it i used 5 as my write address and had to remove a byte swap on the scale head itself. thank you for the help. 

 

[Gabriel Franco]

Modbus addressing can be a little tricky, in your case it could be offset by 1, so try address 0. 

It´s higly recommended to use any PC Modbus software for easy testing.