Idec Pentra and modbus

[thejoker954]

Hi I am trying to get modbus RTU working with my Idec pentra (FC5A)but I'm having a few problems. My biggest is that the modbus address for my data registers are bigger than any simulator takes i.e. modscan32. for example i want to read register d7555 which modbus address is 407556 according to idec but the different sims i've used only go up to 65535. am i supposed to convert the address to hex or something? also The fc5a is supposed to be a slave and while it has the option to turn the port to slave or master I get timeout messages even with all my settings matching do i need to change my pinouts on my cable?

 

[danw2]

Modscan32 will address decimal 47555. The leading 4 is understood as an area of memory used by the 03 command. Do not use the leading 4 in the address in Modscan32.

There numerous reasons you could have timed out.

1) What are the pinouts on your PLC side? The other side is presumably the PC COM 1 port?

2) Have you gone through the connection setup?
Your settings in Modscan32 are?
Your settings in the PLC are?

3) Have you assigned a slave address to the PLC? Does that slave address match the device ID in Modscan32? That device ID is?

4) Have you selected 03 Holding Register in Modscan32 as the Modbus Point type?

5) In Modscan32 reduce the "length" to 2, to diminish the amount of screen 'noise' created by updating multiple registers that you're not interested in.

6) What format is the data in register 47555? floating point real or integer?

7) The table of addresses in the work space in Modscan32 lists register addresses in decimal, so that's an indication that you should be able to use the decimal 7555 in the address

Dan

 

[thejoker954]

Ok I figured out why I was timing out, I was using the wrong setting on my cable. Thank you danw2 for explaining about the two leading digits, my manual mentioned nothing about them being the command code. I can now successfully query my PLC with Modscan32.