The output string is:
▒~▒▒~▒▒~▒▒~▒▒~▒▒~▒▒~▒▒~▒▒~▒▒~▒▒~▒▒~▒▒~▒▒~▒▒~▒▒~▒▒~▒▒~▒▒~▒▒~▒▒ffx▒f▒x▒x`▒x▒x▒x▒`▒x~x▒▒x▒▒x````▒````▒x~xx▒x▒f`▒x▒
And I know that over RS232 the output should look similar to:
ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿSITE NAME,24/07/18,13:15:00,60,0.000,0.000,2.911,2585,
The time may change, as well as the last two numbers but the rest of the string should be consistent. Is there a way to figure out the character set that was used?
It is written in RS-485 Wikipedia as follows.
Protocols
RS-485 is not a protocol; it's simply an electrical interface. Although many applications use RS-485 signal levels, the speed, format, and protocol of the data transmission is not specified by RS-485. Interoperability of even similar devices from different manufacturers is not assured by compliance with the signal levels alone.
If the specifications of the device you are trying to connect are not documented, you only have to look it up with a measuring instrument such as an oscilloscope?
Your Problem might be having selected the wrong baud rate. Check your manual!
Related
I am working on making a custom controller for an aquarium light. I was able to figure out how to adjust the light's internal clock, and I was able to capture some of the communication, and I found this timecode 545f0d31574d52565951607631 which translated to ascii from hex becomes T_ 1WMRVYQ`v1. I know for sure it's the timecode, because it works as expected.
Anyone know what it is? Is it BLE specific? anyone know how to alter it?
I'm pretty sure the first 4 numbers are not part of the code, but a indicator for the device.
Edit:
It is BLE. I should have been more clear. It does most of the transmission on UUID 1000, with the characteristic uuid being 1001. The device doesn't have a built-in clock that I can see. It turn's on and off at the times I specify in the developer’s app. After a power failure, it "resets" to midnight. I know that value is the timecode, because when I input it using gatter tools, I can see the light reacts accordingly. I added a photo of it updating. –
You hint that that this is a Bluetooth Low Energy (BLE) device.
If it is BLE, then the UUID of the characteristic might be in the 16-bit UUID Numbers document. If it is a custom characteristic, then it will not. Official characteristics have the base address of 0000xxxx-0000-1000-8000-00805F9B34FB and only the four missing values are documented.
The specification for how time can be shared over BLE is documented in the GATT Specification Supplement if it is a Bluetooth SIG adopted characteristic.
It might be helpful if you update the question with what this values gives as the value on the light's internal clock.
I'm trying to pick up some serial comms for a new job I am starting. I have done some reading which has helped a lot however, a lot of the reading tells you about the specification of serial comms and what everything is, but not when is best to use particular options.
My searches for this information so far only seem to pull in the spec; perhaps as a novice I am searching for the wrong terms.
My questions then!
Baud Rate - I have read this is signal changes per second and is often mislabelled as bits per second. Is this essentially bits per second including the frame data if asynchronous, and actually bits per second if synchronous?
Parity - Even/Odd.. Is there any difference at all between the two? I'm thinking in terms of efficiency or similar. Does this only still exist for compatabilities sake?
Stop Bits - I have read so far you can have 1 or 2 stop bits. In C# there seems to be an option for 1.5 too. I can't find anything on why you would want/need more than 1.
If anyone can advise on these points, or point me to some recommended reading material I would be very grateful.
Thanks for reading.
edit: typo
You very rarely have a choice, you must make it compatible with the settings that the device uses. If you don't know then you need to look in a manual or pick up a phone. Do keep in mind that it is increasing very rare to work with a real serial port device, one that uses an UART. Most commonly you actually talk to an emulated serial port, implemented by a USB or Bluetooth device driver. The settings you use don't matter in such a case since the actual signaling is implemented by the underlying bus.
If you can configure the device then basic guidelines are:
Baudrate is directly related to the length of the cable and the amount of electrical interference that's present. You have to go slower when you get bit errors. The RS-232 spec only allows for a maximum of 50 ft at 9600 baud.
Parity ought to be used when you don't use an error-correcting protocol. It does not matter whether you pick Odd or Even. Odd people pick odd, it's their prerogative.
Stopbits is usually 1. Picking 1.5 or 2 help a bit to relieve pressure on a device whose interrupt response times are poor, detected by data loss.
Databits is almost always 8, sometimes 7 if the device only handles ASCII codes.
Handshaking is an important setting that never stop causing trouble since many programmers just overlook it. Modern computers are almost always fast enough to not need it but that's not necessarily true for devices. The most basic stay-out-of-trouble configuration is to turn DTR on when you open the port and to tell the device driver to take care of RTS/CTS handshaking. Xon/Xoff handshaking is sometimes used, depends on the device.
A good 90% of the battle is won by implementing solid error checking. It is almost always skimped on, bad idea. Very important for serial port devices since they have no error correcting capabilities themselves and very weak error detection. Always make sure that you can detect and properly report overrun, parity and framing errors. And test them by getting the settings intentionally wrong.
Here is a question I've been trying to solve since quite some time ago. This does not attain a particular languaje, although it's not really beneficial for some that have a VM that specifies endianess. I know, like the 99.9999% of people that use sockets to send data using TCP/IP, that the protocol specifies a endianess for the transmission elements, like destination address, port and such. The thing I don't know is if it requires the payload to be in a specific format to prevent incompatibilities.
For example, let's say I develop a protocol that is not a presentation layer, and that I, due to the inmense dominance that little endian devices have nowadays, decide to make it little endian (for example the positions of the players and such are transmitted in little endian order). For example a network module for a game engine, where latencies matter and byte conversion would cost a noticeable amount of time. Of course the address, port and all of that data that is protocol related would be specified in big endian as is mandatory, I'm talking about the payload, and only that.
Would that protocol work out of the box (translating the contents as necessary, of course, once the the transmission is received) on a big endian machine? Or would the checksums of the IP protocol or something of the kind get computed wrong since the data is in a different order, and the programmer does not have control of them if raw_sockets aren't used?
Since the whole explanation can be misleading, feel free to ask for clarifications.
Thank you very much.
The thing I don't know is if it requires the payload to be in a specific format to prevent incompatibilities.
It doesn't, and it doesn't have a way of telling. To TCP it's just a byte-stream. It is up to the application protocol to decide endian-ness, and it is up to the implementors at each end to implement it correctly. There is a convention to use big-endian, but there's no compulsion.
Application-layer protocols dictate their own endianness. However, by convention, multi-byte integer values should be sent in network-byte order (big endian) for consistency across platforms, such as by using platform-provided hton...() (host-to-network) and ntoh...() (network-to-host) function implementations in your code. On little-endian systems, they will do the necessary byte swapping. On big endian systems, they are no-ops. The functions provide an abtraction layer so code does not have to worry about that.
I'm currently developing a small application for monitoring the power / current our solar collector is generating.
The array is connected to 3 inverters. Every inverter has a RS232 interface, transmitting one Line of information(its current status) every 10 seconds.
Since I want to do the monitoring using a device only having one serial port, I need to come up with a way to be able to read the data from all of the inverters in parallel.
I don't need to send anything to one of the inverters!
Is it possible to just connect 3 RS232 wires in parallel to one serial port? Collisions will be pretty unlikely since every inverter is transmitting only 64Byte / 10seconds ending with a newline, so I could check for variable line lengths to detect collisions.
I'm sort of chuckling at doomsday and wacky answers that so often pop up on stackoverflow...
But anyway, in years gone buy I have used paralleled RS-232 transmit lines using diodes and it can work fine for situations where collisions are unlikely. In one particular application I used this technique there were two input terminals where a user could key in simple commands to control the system (a specialized security system) and it was very unlikely that two people would be trying to control it at the same time from the two different terminals. Amazingly enough there are no problems with voltage levels with most RS-232A receivers I tested at the time and they tolerated the signal characteristics (no negative voltage) that result from the simple use of the diodes in series with the TXD signals. However, if I had to do this again I would likely add a simple pull-down resister and capacitor to ground with a diode between RXD and the cap in a sort of charge pump configuration or a pull-down to negative going handshake signal to ensure the "OR'd" input signal goes truly negative since the RS-232 spec defines +3 to -3v as invalid.
In any case, I would recommend not using this technique except in very specific, limited, and non-mission critical cases and would not use it in the case where you have multiple devices sending information at a programmed interval as in the case of the OP or where there is a software handshake.
In can be a simple solution to the problem of not enough serial input ports but only in a very limited set of environments.
No, you should NOT connect 3 serial output port in parallel. If you do that you are probably going to broke the RS232 output circuitry of your inverters.
You have 3 RS232 outputs, so you need 3 RS232 input, then you can manage these 3 input the way you like: maybe you can buffer the data from each input, and reoutput the data on a single RS232 output, to be connected to your monitoring device.... but you should add some code in the data flow to differentiate the data coming from the 3 inverters.
Maybe you can use some kind of IC that do the job for you, I'm not sure, but maybe that some IC that multiplex multiple RS232 input on a single RS232 output already exist.
Try this search: rs232 port input multiplexer on Google
Or, if the monitoring device is a Window computer, you can use 3 serial-to-usb converter: that will create 3 virtual COM port on your computer and you can read data from them with any software.
Update
About the hypothesis of securing the output circuitry using diods to block reentering current, I don't think it's going to work...
Many year have passed by since last time I've used an RS232 link at low level (so maybe I'm wrong) but I think that there is some kind of handshake going on between RS232 input and output port (speed to use, parity, stop bit...).
Each RS232 port have inputs and outputs signal, both for data and for transmission control, so your multiple RS232 outputs does have some input signals, and your single RS232 input does have some outputs.
This mean that your input monitoring RS323 port is going to try to make a handshake with 3 RS323 ports at the same time... and the 3 RS232 ports are probably going to respond at the same time... so I think it's not going to work.
Other than that if you place diodes on your output, you are going to loose 0.7v, I don't remember the tolerance on signal level of RS232, but maybe that 0.7v can be relevant.
What are the implications of using a half-duplex serial connection versus a full-duplex one? What happens if both sides try sending data at the same time? Do you end up with corrupt data arriving on both ends? Does flow-control help you with this?
On the line the data will be garbled, which may or may not lead to devices receiving the garbled data. Sometimes this will be used to detect that the transmission failed due to a collision.
Normally you wouldn't use half-duplex in the same way as full-duplex to send single characters in asynchronous mode. Rather you'd use some packet protocol which determines who has the right to send at which times, and which includes some checksum (usually a CRC) to detect corruption.
Flow control doesn't help much for this. It's purpose is to ensure that the receiver is not overrun by to much data. There is software flow control which uses the ASCII characters XON and XOFF to start and stop transmission, and hardware flow control which uses the RTS (Request To Send) and CTS (Clear To Send) control lines. XON/XOFF-style software flow control won't work with half duplex.
These days you don't see half duplex with ordinary RS-232 and modems (I used it with acoustic couplers in the eighties, it was rare even then). But it is common for RS-485, which is used in industrial control with various protocols. There are also many other data transmission standards which operate in a half-duplex way, mostly when there are more than two devices attached to the same line (ancient 10base2 Ethernet, CAN, LIN, FlexRay, I2C, ...).
My God, where did you find a half-duplex line in this day and age?
Anyway, the answer is that if both ends drive the line, it gets all confused. For this reason, there are specified ASCII characters lie Clear to Send and Data Terminal Ready (CTS and DTR) that are used to make a handshake. See this tutorial for more.
Augh, I should have gone to bed. Tutorial right, me stoopid.