I have a Precia Molen i30 weighing indicator. I am communicating with this indicator via Modbus 485 using an OPC software (kepware). I have set all the Parameters. According to Manual the Gross Current Weight is on the ADDRESS=256 and data type is 32 bit signed integer. I have set address 300257 or 400257 and data type "Double Word" in my OPC software. With this address communication between my OPC software and weighing indicator is OK but the value coming in my software is not same as displaying on indicator. e.g.,
when value on weighing indicator=0 then value in my Modbus Software=0,
when value on weighing indicator=10 then value in my Modbus Software=655360,
when value on weighing indicator=7160 then value in my Modbus Software=468285400 and when value on weighing indicator=50270 then value in my Modbus Software=3294494720.
Please tell me what might be the problem.Thanks
You have an endianness problem.
When the device indicates 10 (0xa) your Modbus master interprets it as 655360 (0xa0000).
Your OPC server is reading both registers 256 and 257 (because it's a 32-bit variable), but it its concatenating the registers in the wrong order. Check in OPC server manual how to swap the register order, and you'll get the correct values.
Related
I'm using Micropython on an ESP32-S3. I'm setting up DMA from an ADC by manually configuring the appropriate registers using mem32. I need to reserve some space in the SRAM1 region of Internal RAM for the linked list of descriptors. i.e. In address range 0x3FC88000 to 0x3FCEFFFF.
Is there something like array.aray() that lets me specify a range?
I assume either drivers or some other internal Micropython plumbing under the hood is already using some of that internal RAM address space, as I see non-zero values in it. I want to make sure my code doesn't stomp on anything being used (or vice versa).
I'm sorry if my question is too easy or obvious. I'm Comp. Science Student (it's my 6.th term).
I'm trying to combine the knowledges that I'm learning from 'Computer Networks and Security', 'Computer Organization' and 'Operating Systems' lectures in this term.
So, I cannot figure out that;
Does a computer or a phone has physical components for each 65535 ports/sockets?
Or
The machine has just one physical component. So that means port numbers are logical representations that can be shown as text-fields (like header entities or json attributes) of a request or something, to say to computer how to handle the request?
I used ports for connections of back-end and android and front-end. I know that a socket is a physical component, I worked 4 months as phone-repairer, I know these. But this makes me confused.
Thanks in advance..
Think of it this way: "the network interface is the phone system, IP-addresses are phone numbers, and socket/port numbers are like telephone extensions. (The network interface is the only physical device.)
Network traffic is carried by so-called "packets" which have various fields which tell the network how they should be routed. The IP-address will get the packet to the proper destination, then the port/socket-number will specify exactly what software process at that destination should actually handle this packet.
While unit testing a Modbus driver I'm writing I experienced the following:
I can read holding registers 0 to 1022.
I can't read holding registers 1022 to 13000. I get an illegal data address error code.
I can read holding registers 13000 to 25000.
I would have expected devices supporting Modbus to behave in one of the following two ways:
Every device supports the full range of addresses from 0x0000 to 0xFFFF.
Every device supports a range of addresses from 0x0000 to N, where N < 0xFFFF.
Do any of you more experienced people know:
Is Assumption 1 or 2 about the expected behavior of Modbus devices correct?
Are there other reasons beside being out of bounds for an address to be an illegal data address?
Both assumptions are false. It's completely up to the device to decide which registers to support. Some devices are nice and support a wide range of registers, even if they're unused. Most that I've used don't, though. They'll use groups of registers, like your device.
Also, not all Modbus devices support all the Modbus function codes. Just because it's defined by the Modbus protocol standard doesn't necessarily mean the device will support it.
The key thing is to stick to the addresses defined in the device's manual. The manual is usually required reading, otherwise you'll just be guessing at the ranges, units, and scaling.
In wikipedia the image of ethernet frame includes a field "inter-packet gap". Other sited I've looked in don't have that field. I don't seem to understand if the gap is predefined according to the protocol or it can be changed using this field.
The default gap between packets is 96 "bit times" (the time taken to send 96 bits on the medium used).
This is sometimes too big or too small in very specialised circumstances, so organisations are allowed to override this by specifying their own.
By including this field, you're effectively telling the recipient, "I'm not going to send anything for n bit times now, please do the same".
Apparently, it's too small for some Ethernet connections on MS Windows and can be changed
here
Consider the following Ladder Program that checks if a connection is enabled (A202.00) then send a message from the PLC to the PC.
The documentation (Omron CX-Programmer) has a severe lack of explanation of the program convention. What I do not understand is:
To send a message from a node to a node. I should need to specify the receiver ID. It seems the function block does not have an option where I can insert an IP address. Am I supposed to MOV an IP address to a DM address (D300) then use it? If that's the case how (IP address has dots in between 4 bytes..)?
Can someone please explain what is S (First source word), D (First destination word) and C (First control word). Aren't they just memory address? E.g. sending content of a memory adress to another memory address?
[EDIT]
What am I trying to do?
I am trying to interface a measuring gauge (controlled through Ethernet by PC/C# application) to a robotic system (no RS232 or serial, no TCP/IP, only has the simplest I/O points) with an Omron PLC. When gauge completes a measurement, the C# app sends a command to the Omron PLC which, according to the command received, switch ON or OFF an output which triggers a voltage flow to the robot's I/O port.
Should I use FINS? What functions/protocol from the PLC I need to know to do this? I do not know so I am testing every function from the documentation. So far, zero progress.
1) All addressing information is encapsulated in the five control words (C -> C+4). C- "First Control Word" is the pointer to the first word in this table of five words you must have stored somewhere in your PLC to set up the communication.
2) First source word points to the first word in your PLC you wish to send. First destination word points to the first address in the PLC/device you wish to send to. In the example , the first control word specifies that 10 words should be sent. You point to the first one and it will send that one plus the next nine addresses as well.
To do this you have to use FINS communication - the PC stores a memory structure similar to the PLCs (CIO, DM, etc) called Event Memory and these are the addresses in the PC you are pointing to. The PC gets a FINS node number and address just like a PLC would - no IP addresses are involved. (see : FINS Manual) FINS is old, however, and has been superceded by things like Sysmac Gateway.
There are much better ways of communicating between PLC/PC, however, depending on what you are trying to do. Are you trying to write an HMI? If so, what language are you using?
Edit :
If you're using C#, I highly recommend you look into Sysmac Gateway and CX-Compolet. This is probably the most flexible, simple, and extensible way to get .NET working with Omron PLCs. If it is at all possible, however, a better way might even be to have the measurement unit communicate directly with the PLC via hardware I/O (relays, DIO, etc).
CX-Compolet, Sysmac Gateway link:
http://www.ia.omron.com/product/family/63/index_l_u.html