Contents. Introduction RS-232 is a standard for serial data communication between computing equipment. This standard dates back to 1962 but has been substantially revised over the years to accommodate changes to communications technology. At a minimum, an RS-232 connection may consist of a single wire connected between two pieces of equipment.
The simplest connection in common usage contains three wires: transmit (tx), receive (rx), and ground (gnd). However, a fully implemented connection can contain as many as 25 wires. Early RS-232 connections were commonly used to connect terminal equipment to modems, so these topics are often intertwined. Data Terminal/Communications Equipment In the world of serial communications, there are two different kinds of equipment:. DTE - Data Terminal Equipment.
DCE - Data Communications Equipment Straight Serial Connections In practice, the distinction between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE) is simply a matter of function. This is an instance where the subjects of modems and serial communication equipment have been mixed together.
Here, the modem can be thought of as the DCE and the terminal that faces a user is the DTE. Years ago, when the use of timeshare computing systems was common, the user would dial a telephone, place the telephone's handset against an acoustical modem, and that modem would be connected to a simple dumb terminal with an RS-232 cable. The typical connection speed was usually 50 baud or 110 baud, though very fast connections could reach 300 baud. As a side note, when the very first IMPs (Interconnection Message Processors) that formed the first nodes/routers of ARPAnet (the ancient predecessor of the Internet), this was exactly the connection system they were using.
This later gave way to other communication systems, but this was the beginning of the Internet. In a more modern setting, imagine a piece of equipment in a very dangerous place, like in a steel processing mill that measures the temperature of the rollers or other steel processing equipment. This would also be a form of what we now refer to as a piece of 'Data Communication Equipment' that we would also want to be able to control remotely. The PC that is used in a control room of the mill would be the Data Terminal Equipment. There are many other similar kinds of devices, and RS-232 connections can be found on all kinds of equipment.
The reason this is called a 'straight' connection is because when the cabling is put together, each wire on each end of the connection is connected to the same pin. Null Modems Often you don't always want to connect a piece of equipment to a computer, but you would also like to connect two computers together. Unfortunately, when connecting two computers with a 'straight' serial connection, the two computers are fighting each other on the same wires. One way to make this work is to connect the two computers to each other with a pair of modems. As explained earlier, this is a very common task, and in the 1980's and early 1990's it was common to have 'Bulletin Board Systems' (BBS) where computers would call each other up with modems and exchange all sorts of information. Now imagine if these two computers are in the very same room. Instead of going through the physical modems, they go through a 'null modem', or a modem that really doesn't exist.
Serial Connector Types
In order to make this work you have to 'cross' some of the wires so when you transmit some information on one end, the other computer is able to detect and receive that same information. In addition to simply allowing a computer to communicate and transmit data to another computer, a null modem connection can be used to 'simulate' the behavior of DCE equipment. This will be particularly important later on with some of the discussion in this series of articles, where you can experiment with writing some of your own serial communication software. In my own experience, I've had to write these 'emulators' in many instances, either because the equipment that I was trying to communicate with wasn't finished, or it was difficult to obtain a sample of that equipment and all that I had available to me was the communication protocol specification. Loopback Connectors Sometimes instead of trying to communicate with another computer, you would like to be able to test the transmission equipment itself. One practical way of doing this is to add a 'loopback' connector to the terminal device, like a PC with a serial data connection. This connector has no cable attached, but loops the transmit lines to the receive lines.
By doing this, you can simulate both the transmission and receiving of data. Generally speaking, this is only done for actually testing the equipment, but can be used for testing software components as well. When this sort of connector is used, you will receive every byte that you transmit. If you separate out the transmission subroutines from the data capture subroutines, it can provide a controlled system for testing your application. Protocol Analyzer General When it starts to get very difficult to examine the serial data being transmitted by the equipment, sometimes it is nice to be able to take a 'snapshot' of the information being transmitted.
This is done with a protocol analyzer of one kind or another. What is done is a modification of the cabling that allows for a third computer to be able to simply read the data as it is being transmitted. Sometimes the communication protocol can get so complicated that you need to see the whole exchange, and it needs to be examined in 'real-time' rather than going through some sort of software debugger.
Another purpose of this is to examine the data exchange for purposes of doing some reverse engineering if you are trying to discover how a piece of equipment works. Often, despite written specifications, the actual implementation of what is occurring when transmitting data can be quite a bit different than what was originally planned. Basically, this is a powerful tool for development of serial communications protocols and software, and should not be ignored. There are common ways to connect a protocol analyzer, which are discussed in the following. One of the most convenient tool to monitor and analyze serial port data is.
This software allows to intercept all serial control codes and record detailed information about them. The data captured can be viewed in all 4 different views simultaneously that is, table, line, dump or terminal mode with each display providing a unique way of representing RS232 analyzer captured data. Y 'Cable' A Y 'Cable' is not just some cable, but also contains electronics - assuming it is not a low quality cable. It is supposed to be placed in between a serial line and it mirrors all signals on a third connector. This third connector can then be connected to a protocol analyzer (e.g.
A PC with some display software): +-+ serial +-+ serial +-+ DTE - Y Cable - DCE +-+ +-+ +-+ +-+ Analyzer +-+ It is recommended not to use a passive Y cable. Such a cable overloads the transmitters at the DTE and DCE, which might result in the destruction of the transmitters. The RS-233 standard requires that transmitters are short-circuit safe. However, modern, highly integrated equipment might no longer be compliant to that particular aspect of the standard. Often, the line going to the analyzer is also just a serial line, and the analyzer is a PC with a serial interface and some display software. The disadvantage of such a simple Y cable solutions is that it only supports half-duplex communication.
Vera Serial Interface Connectors
That is, only one site (DTE or DCE) can talk at any time. The reason for this is that the two TX lines from the DTE and DCE are combined into one TX line going to the analyzer. If the DTE and the DCE both send at the same time, their signals get mixed up on the third line going to the analyzer, and the analyzer probably doesn't see any decode-able signal at all. See for an example of some simple circuitry for a Y cable.
More advanced Y cable solutions provide the TX data from the DTE and DCE separately to the analyzer. Such analyzers are capable of displaying full-duplex communication. Advanced professional systems not only display the decoded digital information, but also monitor the analog signal levels and timing. Man-in-the-Middle In this scenario the analyzer sits in the middle between the DTE and DCE.
It is basically some device (e.g. A PC) with two serial interfaces. The analyzer mirrors each signal from one site to the other site, and also displays the traffic. +-+ serial +-+ serial +-+ DTE - Analyzer - DCE +-+ +-+ +-+ In principle, a simple version of such an analyzer can be built with any PC with two serial interfaces. All that is needed is some software, which is not too difficult to write. Such a device will, however, lack a convenient feature.
Professional analyzers are able to auto-sense the speed of the serial communication. A home made solution needs to be configured to match the speed of the serial communication. Professional devices are also optimized to ensure minimal delay in the circuitry.
Also, a simple homegrown, PC-based analyzer can't be used to analyze faults due to signal voltage level problems. Nevertheless, any kind of protocol analyzer is much better than nothing at all.
Even the most simple analyzer is very useful. Others See for some more information. Breakout Box.
Honeywell / Ademco Alarm Panels with RS-232 Interface Introduction This plugin is for Honeywell and Ademco Panels that have either an RS232 built into them, or the ability to add one on through a module such as the Honeywell 4100SM. This plugin is not designed to work with an third party add on module such as the IPDataTel or AD2USB modules. The protocol it talks over RS232 is Honeywell's proprietary one.
This plugin performs several functions:. It can arm or disarm the system from Vera. It exposes all sensors in the system to Vera. It exposes the system state (armed or disarmed) to Vera.
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It reports on current maintenance status. It can also be used to do some routine functions. Physical RS232 Connection This will be different for each panel used.
Development of this plugin was done on a Vista 128BPT panel, which has a header on the alarm panel board. In this case, the RX and TX pins were wired to a standard RS232 9 pin connector and connected to a FTDI serial to USB adapter.
The panel has been heavily tested in this configuration, however, each panel or add-on module will have a different method. However you connect your Vera to the RS232 of a Honeywell or Ademco Alarm product, the protocol should be the same. There are 3 ways to connect the panel to Vera:. Direct connection using an USB RS-232 Serial Adapter like one. For best compatibility with Vera, I recommend a serial adapter with FTDI or Prolific chipset.
Via Ethernet using a Serial-to-Ethernet Gateway like one. Wireless using an WiFi RS-232 Serial Adapter like one. Installation & Setup. For UI4 click.
For UI5 click. Discussion Discussion for this Luup plugin is on the MiCasaVerde forum.
I had to power cycle my Vera 3 today to move the power plug and now I've lost the USB/Serial port connection AGAIN. Just about every time anything at all happens the serial port goes away and does not want to recover.
I've reloaded all the LUUP files, reloaded LUUP, power cycled, Rebooted, everything I can think of to no avail. When Vera restarts it says Select Serial Port. In Develop Apps the Serial:Port selection shows unavailable. I know the USB is working, the USB Logging appears to be working - although that also went away in the original power cycle Does anyone have a fix or work around for this problem? I guess I'm going to have to get cracking on building the Ethernet Gateway, this is ridiculous. Hi, I triede it with version 1.2 and it worked fine, but a had to use the serial port in the vera for a RF device i changede it to ethernet version. Now i dont use the RF device anymore, in the meantime i was on version 1.3.
So i decieded to upgrade to 1.4 and use the serial GW. None of my many Uno's Nano's and even a MEGA worked, the Vera couldnt see any USB, so i triede also with a powered HUB, different types of USB cables, still nothing. The i went back to the 1.3 version still nothing. Then i made a complete reset of the vera nad connected the Serial GW again, nothing. Hmm, thinking if i should try the old 1.2 again or just keep the ethernet GW shield.
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