Re: RPGLE Socket Communication with Modbus

Hi Russel,

Looked over your code and one potential issue sticks out, your
communication is only in one direction. Could your device be expecting to
be sending back an acknowledgement before it processes any
messages/commands? Have you tried to translate your message into hex prior
to "callp Translate(reqlen: request: 'QTCPASC');"? In my experience
communicating with devices, be it over RS232 , or USB, the device is
expecting it's own communication protocol to be followed, in addition to
CRC32 check/bits being included in the message for instance. While you
could very well be sending data to the device, the device won't respond in
an expected fashion because it's communication protocol isn't being
followed.


Regards,

Adam B. Dodson
IT Dept.
Software Developer, Systems Administrator
Powercon Corporation


On Wed, Jul 10, 2019 at 4:24 PM Scott Klement <rpg400-l@xxxxxxxxxxxxxxxx>
wrote:

Hi Russell,

My thoughts are in-line:

Currently I have the pick to light device plugged into COM port 7 of my

PC via USB.

I am then using demo version of TCP-Com software to allow my PC to act

as a server to which my Socket Client program on the Iseries can connect to
and communicate with.

I'm not familiar with TCP-Com software, but it sounds like a proxy of
sorts to allow you to use TCP/IP communications to communicate with an
RS-232 device. FWIW, there are also hardware devices that do this,
small devices you can plug into the RS-232 port of whatever machine
requires the RS-232 communications (I've used them on printers and
scales) and then you plug into ethernet on the other end, and it acts as
an TCP/IP server, eliminating the need for the PC. Might be worth
considering.

I am using the CLIENTEX1 tutorial program as a base for my personal

socket client program with the major changes being no entry parameters and
no receiving of data (For now I simply want to write to a single register
and get something to happen on the device).

There is no concept of a "register" in TCP/IP programming. I'm guessing
that this is specific to the particular machine you are talking to
("Modbus"? whatever that is.)

I would not recommend using CLIENTEX1 as a base for anything. It is
meant to be a very beginner example, to allow you to understand some
basic ideas of TCP/IP programming. Subsequent examples build on this,
making it more robust.

When I run my program I have confirmed that the connection is

established and program runs all the way from beginning to end but nothing
is actually happening with the device.

I believe the issue is with what I am sending (request variable) and I'm

unsure if I should even be performing translations to ASCII as well.

This depends on what the target machine is expecting to see. A TCP
channel is just a communications medium. It enables communication to
occur, but it doesn't tell you what specifically needs to be communicated.

Asking us whether your data needs to be in ASCII, or what to put in your
variable would be analogous to calling up your telephone provider (such
as AT&T or Verizon here in the USA) and asking them what language you
need to speak when you call your friend. They aren't going to know
that! You have to work it out with your friend.

Likewise, we aren't going to be able to tell you what you need to
send/receive to your Modbus device. You'll need to look in the docs for
the Modbus device, or work it out with someone who has expertise with
those devices.

Below is a sample of my program with further details. Does anyone have

any experience with this and can provide me with more direction?

I would like to send the value 1 to 16 bit input register 6302. My slave

ID should be default 1.

Sorry, I have no idea what "16 bit input register 6302" is. Again, this
sounds device-specific. See above.


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