Host Engineering Forum

General Category => ECOMs and ECOM100s => Topic started by: harncw on March 11, 2011, 12:51:02 PM

Title: The H0-ECOMM100 never responded to my incorrectly formated ModbusTCP request.
Post by: harncw on March 11, 2011, 12:51:02 PM: Granted the error was on my side... (I had my bits and bytes incorrect)
However the ECOMM100 maybe should have responded with something.

Firmware 4.0.269
Booter 4.0.165

From Wireshark:

No. Time Source Destination Protocol Info
   664 33.178201 192.168.1.109 192.168.1.100 Modbus/TCP query [ 1 pkt(s)]: trans: 1; unit: 255, func: 15: Force Multiple Coils.

Frame 664: 69 bytes on wire (552 bits), 69 bytes captured (552 bits)
Ethernet II, Src: Intel_4f:a6:32 (00:07:e9:4f:a6:32), Dst: HostEngi_20:e9:db (00:e0:62:20:e9:db)
Internet Protocol, Src: 192.168.1.109 (192.168.1.109), Dst: 192.168.1.100 (192.168.1.100)
Transmission Control Protocol, Src Port: xinuexpansion4 (2024), Dst Port: asa-appl-proto (502), Seq: 1, Ack: 1, Len: 15
Modbus/TCP
   transaction identifier: 1
   protocol identifier: 0
   length: 9
   unit identifier: 255
   Modbus
   function 15: Force Multiple Coils
   reference number: 3104
   bit count: 24
   byte count: 2
   Data

0000 00 e0 62 20 e9 db 00 07 e9 4f a6 32 08 00 45 00 ..b .....O.2..E.
0010 00 37 79 2e 40 00 80 06 fd 70 c0 a8 01 6d c0 a8 .7y.@....p...m..
0020 01 64 07 e8 01 f6 b6 ec 79 21 1d ec c0 a2 50 18 .d......y!....P.
0030 ff ff 05 cf 00 00 00 01 00 00 00 09 ff 0f 0c 20 ...............
0040 00 18 02 00 00 .....
Title: Re: The H0-ECOMM100 never responded to my incorrectly formated ModbusTCP request.
Post by: Greg on March 15, 2011, 10:32:17 AM: Is this Wireshark trace a sample of the incorrectly formatted telegram your ECOM100 didn't respond to? Or is this a correctly formatted one that it does respond to?
Title: Re: The H0-ECOMM100 never responded to my incorrectly formated ModbusTCP request.
Post by: harncw on March 15, 2011, 10:47:09 AM: The former.

I'm showing an improper ModBusTCP request, the PLC never responds to this request.
the bits are 24 and the byte count is 2. (there are typically 8 bits in a byte, not 12)

When I send this bad "telegram" (I guess that term can be used) to the PLC I do not get a response.

I'm not positive I really should get a response to bad request. However I noticed this as I was debugging my side, and I wanted to point out that when I send this bad request I get no response.

Granted, I should definitely not send bad requests, however maybe when I do, I should get a response?

It's debatable, I just noticed this and wanted to point it out.
Title: Re: The H0-ECOMM100 never responded to my incorrectly formated ModbusTCP request.
Post by: Greg on March 18, 2011, 02:25:07 PM: Thanks for the heads-up on this. Yes, we discovered we have not been verifying the byte count on FC15 or FC16. :o We will add a verification for these. Since this is a hole in our code, send me an e-mail (support@hosteng.com) with shipping address and I'll send you a HOST T-shirt. Specify size. ;D
Title: Re: The H0-ECOMM100 never responded to my incorrectly formated ModbusTCP request.
Post by: harncw on March 18, 2011, 03:51:57 PM: Hey cool I just so happen to wear shirts! ;D

I appreciate Host taking this relatively minor issue seriously. I find that seemingly trivial things can point to valuable information.

Hmm now I'm going to try and break your toy in other ways, maybe I can outfit my whole family in Host T-Shirts!
Title: Re: The H0-ECOMM100 never responded to my incorrectly formated ModbusTCP request.
Post by: Controls Guy on March 18, 2011, 08:12:54 PM: Quote
Hey cool I just so happen to wear shirts!

So YOU'RE the one! :D
Title: Re: The H0-ECOMM100 never responded to my incorrectly formated ModbusTCP request.
Post by: b_carlton on March 18, 2011, 08:18:12 PM: Yeah, I understand. You keep getting thrown out of restaurants then it finally dawns on you what the sign means. I started wearing shoes at that same time.