RE: RPGLE Socket Communication with Modbus

Thank you everyone. I have contacted the vendor of the device to try and make sure I am following the expected communication protocol and things of that nature. Since the issue looks to me to be only with the request I am sending perhaps they can look it over and confirm I am meeting the expectations.

Thank you again for the advice




Russell Wesh | Applications Supervisor
Sumitomo Drive Technologies
Sumitomo Machinery Corp. of America
Tel: +1-757-485-3355 ext. 8633
www.sumitomodrive.com | How are we doing?





-----Original Message-----
From: RPG400-L [mailto:rpg400-l-bounces@xxxxxxxxxxxxxxxxxx] On Behalf Of Adam Dodson
Sent: Thursday, July 11, 2019 10:57 AM
To: RPG programming on IBM i <rpg400-l@xxxxxxxxxxxxxxxxxx>
Subject: 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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