Does anyone know of a scheme whereby MODBUS addresses can be automatically set? In my situation I'll have a number of slaves power up and need some automatic way of assigning them addresses.
I know this is an old post, but I just came across this and thought I would give my answer just in case someone is attempting to do this now or in the future. If the goal is to assign a slave ID to a new slave (and you are developing the firmware for the slave devices), you can have the ID stored in a holding register that you can write a new ID to. This does require that:
You know the ID already. Maybe have all new slaves have a default ID, say ID = 1, so you know the ID beforehand.
You can only add one slave at a time and must change the ID before adding another slave to the network.
For example: Connect and power up the first slave device, which has a default ID of 1. Send a write command that will change the ID to 2 and send the master a response (using the slave ID of 1 in the response so it doesn’t timeout). Now the slave ID is 2. Next, add the next slave to the network, which it’s ID is 1. Now you have two slaves on the network with unique IDs. Just repeat as many of times that you need to.
Are you talking about SLAVE ID's? If so, that's just not going to happen... The SlaveID is vitally important for the Client to be able to address said slaves on the serial network. (RS485 serial network, presumably...).
So, there is no way to even send out a Modbus message and address it to SlaveID 1, and then somehow get that device to be SlaveID 1, because ALL of the devices would attempt to respond, in that case. Not to mention, there is NO method in Modbus to ASSIGN a Slave an ID... On the flip side of this...
Are you talking about performing some type of query to ask the slave devices which Modbus REGISTERS they have? Again, there is no Modbus way to do this, but with some code, you COULD query 40001, and if you get an error 2 back, then you know that register is not available. If you then loop through all of the registers, keeping track of which ones returned non-error, well--then you COULD do a form of "auto-configure", but... In all honesty? I would NOT recommend this, and I don't see a lot of value to even DOING this, because you not only have to know the REGISTER numbers, you have to know WHAT THE DATA IN THE REGISTER ACTUALLY MEANS!
What exactly are you trying to do anyway? Perhaps there is another way to accomplish this goal?
What you think you want: automatic Slave ID assignment in Modbus RTU.
What you actually want: constant, common Slave ID with Modbus TCP.
In a nutshell, all your Modbus Slave ID's get set to a fixed, common value and then you bridge them with a TCP stack that supports things like link-local addressing or DHCP. Then the TCP address assignment can be dynamically handled while preserving a constant SlaveID for each unit.
There are three broad options here depending on what hardware you already have:
There are commercial off-the-shelf devices (such as this) that can emulate TCP over RTU. I've not delved too deep into what they support and how well they work.
You could also add a whole ton of TCP to RTU bridges which will have built-in management for the TCP/IP layer and then use real Ethernet cabling. For a lot of devices, this could get expensive fast, but with Ethernet you have all sorts of bonus features like basically unlimited distance and improved CRCs. If you're looking to do this on the cheap, grab a dual-port Linux SBC (such as this or this) and throw mbusd (from here) on it.
If you have access to or are developing the firmware yourself, you could adapt something like uIP (simpler) or lwIP (faster) to communicate over RS-485 (UART). This would certainly be the cheapest option. Note that you should also have the ability to detect collisions on RS-485 to implement an IP stack correctly -- this involves echoing the receiver at all times and checking that the data-in and data-out match.
Related
I'm trying to figure out, how to connect two hm-10 module, when I do not know the slave MAC address. Imagine you have an electric longboard and lost you remote. You got yourself a new one and now want to pair with the board.
In the data sheet I cannot find any useful functions, to make this process easy.
I thought about making an unique name of the slave device and by making a pairing button on the master device. The pairing button would set the master device in the pairing mode (AT-ROLE1, AT+IMME1 in order to execute AT+DISC?). The results of the AT+DISC? command would be saved to an array and after finding the unique name of slave device, the index of the device/MAC address would be saved and used as a parameter for establishing the connection.
I'm using the firmware version v707.
The problem is, I do not find this solution as elegant and I think there must be a better way to do that, but I cannot find any information about it. Did anyone tried to do that and maybe has some insight? I'd very much appreciate it.
Only way I can think of on the HM10 is setting a unique name and scanning for that name.
Another way I have seen is some devices allow you to see service UUIDs in the advertising information so you can connect to the device that has the desired service UUID. But this doesn't seem possible on the HM10
I am in the middle of building a custom Canbus IO module based off an Atmega2560 chip. The module will have 10 high current outputs with pwm control and current feedback, 20 digital inputs, 5 analog inputs and 4 0-5v analog outputs. I've been working on figuring out the J1939 message structure I'll be using. These modules will be slave devices being controlled by a master ECU. Since more than one of these modules may be on the same network, I've added a CAN Address switch to each module so the user can select the CAN ID 1-255 of each unit. The plan was to have each module broadcast the state of all the digital inputs in a single CAN message. If I Select 0xFF00 as the PGN ID and then use the 8 bytes to represent the state in bit form for the status of the input for that particular module then how does the master know which module the message came from? Is the module address in the CANbus message?
I've been looking at the arduino CANBUS examples and it looks like you can filter based on PGN but I don't see anything to filter based on source address or destination address.
Can someone provide some clarification on how I might do this?
Yes, as doynax mentioned, the 8 least significant bits are always reserved for the source address of a node. If you will be placing this network on a vehicle's CAN bus, it is important to note that if you do not claim a source address on the vehicle bus, you may get a NAK from the main ECU whenever you try to place foreign information on the bus.
In order to prevent this issue, you may have to do an claim address procedure for each custom node on your network. This is where you send out PGN 60928 as a broadcast (destination address 0xFF) and every node on the network should respond on that PGN with their own source address (assuming all nodes comply to this specification, not all do). If a common source address is seen on the replies, then you know that it is not available.
See the following slideshow for more information starting on page 39
J1939
I am engineering two BLE devices, a central and peripheral. (Using a PSoC 4 BLE, not that it matters)
There will be a lot of these in a small space, maybe up to 8 within range, but hundreds of peripherals and tens of centrals all coming and going, with no particular rhyme or reason behind which one central/peripheral the user will want to pair at any given time.
I also have an unrelated technology that makes it very easy for the user to move a blob of data from the central to the peripheral of their choosing. I believe this will make pairing much easier in most but not all scenarios.
I figure the non-BLE blob would contain at least the central's mac address, and maybe a randomly generated pin or shared key. Because the blob can only go from the central to the peripheral, the receiving peripheral is really the only device that knows the addresses of the two devices that are supposed to connect.
However, as I understand it, peripherals can't make outgoing connections. I can't swap roles because I still need the BLE search to work the traditional way.
I can think of a lot of ways to get this done, but I'm very interested in hearing the opinion of someone who has worked with BLE long enough to know what might fit best (or if I'm wrong about some assumption).
Some constraints I'm working with:
The peripheral is battery powered.
The usual search and pair method must also still work.
My own half-baked ideas:
Make the peripheral able to be a central too, but then does that
introduce more nuances and complications?
Broadcast from the peripheral, "whoever has X mac address,
please connect to me"
Put a similar message in the advertising packet and increase advertising
rate.
Directed advertising similar to above?
You could let the "non-BLE blob" contain a static random address which the central generates. After the peripheral receives that, it starts advertising with that static random address. The central is also configured to initiate a connection to that particular static random address. Will this work?
Being somewhat of a newbie I was wondering if there is a way to hard-code something on a peripheral that would only allow a single unique central/master to connect.....?
i.e. / eg
I have the ‘simple chat’ Arduino app on a RedBearLab Blend-Micro (which is for all intensive purposes the same as a Arduino Uno with a BLE shield) and I only want one single / unique phone to BE ABLE TO connect with it and therefore work with it.
My understanding is that the GAP handles security features during a BLE connection.
Therefore, is there some way to ‘code’ the peripheral device in / below one of the following includes:
spi.h ?
boards.h ?
EEPROM.h ?
RBL_nRF8001.h (or similar) ?
Other?
Didn't quite get an answer from Restricting the BLE peripheral device to connect to only one Master
OR
Am I stuck with EVERYTHING connecting but coding the peripheral in some other way in a GATT profile (I think) to ONLY do something with a predefined unique central/master (how/where to code?).
Many thanks for thoughts in advance
Being somewhat of a newbie I was wondering if there is a way to hard-code something on a peripheral that would only allow a single unique central/master to connect.....?
Theres the "Advertising Filter Policy" as specified in the Bluetooth Core V4.0 specification. Its a Byte in the Advertising Parameters as specified in Section 7.8.5 LE Set Advertising Parameters Command.
For example the value 0x02 reads Allow Scan Request from Any, Allow Connect Request from White List Only.
Then theres section 7.8.16 LE Add Device To White List Command.
That said, if your device confirms to the Bluetooth 4.0 specification, it should support these HCI commands. However there might be functions that simplify these procedures, wrapping those HCI commands for easier use. Check the Documentation of your device for such methods.
Good Luck!
I was asked to answer this question via email. It's been almost a year since I quit working on BLE. So I only answer this question based on my memories.
Basically #dominik has it right.
If the device is freshly new, it should advertise normally (without setting the whitelist only bit), then any central device could connect and bond. Once it is bonded, you should save this bonded flag and the bonded master's bd_addr to EEPROM. If the next time the master is lost, you will advertise with that white-list-only flag set. If a new central tries to connect, you could verify if its address is the same as your master.
I don't have the BLE spec at hand and I kind of forgot a lot about BLE already. Probably the spec says somewhere that if a central sees a peripheral device is broadcasting with white-list-only flag set, it wouldn't try to connect if it doesn't recognize that peripheral device. This saves both some effort.
But a master could always initiate a connection to your peripheral device regardless the white-list-only flag. So checking if the connecting central device's address is the same as your previously bonded master is the last resort.
[Update]
I used CSR1010 chips. I remembered that the BLE stack actually allows me to insert a list of bd_addr to the white-list data structure maintained by the stack. Then, with the white-list-only flag set, the lower-level stack layer will help you filter devices that are not in that white-list without your knowing.
However, you can always filter bd_addrs from your application code.
There's a old piece of software we run in our company that manages RFID cards tapping in/out to open doors.
We want to create an app who identifies who just touched in on a specific place (we have the id for that) and grab their 1st name, to say "Hi [NAME]" on a screen.
As I mentioned, the software is quite old and there are no APIs. It communicates with the RFID hardware via a serial port (COM1).
I was wondering if the best way to get the data I need is to somehow intercept the COM1 traffic and extract/look for the data I want.
Does this sound like the best way to go about it? Would it work, or would it be impossible to get names and numbers from the data being transferred?
Cheers,
Andre
Can you configure the software to use a port other than COM1, or configure the hardware so it's physical serial port is assigned to a different COM port?
If so, take a look at com0com. It's a Windows driver that creates two COM ports on your PC with a virtual NULL modem between them. Data going in on one side comes out on the other.
Here's how you'll set things up:
RFID Reader connected to physical COM port (COMx)
your program bridging COMx to COMy and sniffing the traffic
com0com linking COMy (for your program) to virtual COM1 (for the legacy software)
legacy software
You'll need to write a program to pass data between COMx and COMy while monitoring it for the information you're looking for. Make it simple yet robust, since if it goes down you're reader will stop working.
A Simpler Solution
If you only need to monitor one side of the communications, create a cable that connects the GND and RX pin of COM1 to another COM port. Now your program can monitor that side of the conversation, without interfering with the legacy software.
Well, generally, you can look at RS232 signals, if that's the way you want to do it. It's tricky because you need to "sniff" the signals, which means buying or making a rig that allows the original signals to go through, and then gives you a way to attach to them as well. And, you need to send the transmit and the receive signals to TWO serial ports (on the RX lines). Then you'll probably want to get some "sniffing" software that allows you to look at what you're getting in time sequence (ideally, with time-stamps). Some cutesy protocols also will use modem lines, so you may need to monitor those as well.
Or, try searching for "free serial port monitor" or "serial sniffer".
Good luck!