Modbus RTU over TCP, bytecount

Ignition
1

I'm having trouble with modbus.

When I do HRS40:10 - is that 10 registers or 5 registers ?

The reason I ask, is that I get a bytecount of 10, when it should be 20, when asking for 10 registers.

When I try with other modbus clients, I get the correct bytecount (20), but not with ignitions modbus driver

All help highly appreciated.

Regards

2

As per the manual:

[DL240]HRS1024:20 Read 20 character string value starting at Holding Register 1024.

@Kevin.Herron can perhaps clarify further, when he wakes up...

3

That's String length in bytes, so it's 5 registers.

4

Thank you.

5

On that note, is it possible to read multiple integer registers?

like [Device]1.HR40:20 ?

I don't see this anywhere in the documentation.

best regards
V

6

Not as arrays, no. Only when addressing a multi-register datatype like Int32, Float, Double, etc...

7

Ok, modbus is new to me.

I'm trying to read from a siemens s7-1200 via modbus rtu over tcp.

I have a struct which have some Int and Uint, and are addressed from 0 to 14

The catch here, is that there is a hydro acoustic modem in between, and the delay is around 20 seconds.
Therefor the RTU

Reading a single integer works fine, but I'm having a hard time reading a block (array) of integers.

Can you point me in the right direction, or simple say it's not possible with this ignition driver.
(it works on other clients)

best regards
V

8

You don't address a block, you just create multiple tags, one for each register or register(s) depending on the datatype, that span a contiguous address range. The driver will read them all in one request.

I'm not sure why the horrendous latency implies RTU.

9

If you have other working clients, then get Wireshark captures to compare.