How to test rs232 modem cable. How to make a null modem cable for flashing receivers yourself
Let me quote from my book:
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Problems with the "firmware" of the receivers: the lack of a COM port, the use of a laptop.
Most of the "old" computers and laptops, purchased more than 5 years ago, always had several COM ports (RS-232). At least there was always at least one "RS-232" connector.
All drawings for this chapter are located in the "USB_PCI_COM" folder.
Rice. D-9_RS-232 Connector on the computer case - COM port (RS-232)
Various external equipment was connected to it: mice, printers, modems, various specialized equipment. Therefore, there were no problems connecting the receiver to the computer for “firmware”. It was enough just to connect, run the program to update the receiver software and calmly do everything you need.
Most modern computers there is no RS-232 connector. This is where problems arise, often very unpleasant ones. In most receivers there is no other way to "firmware" other than using "RS-232". And not all receivers have a “USB” input for connecting an external flash drive.
And sometimes there is another problem: the laptop has a COM port, but it works with receivers of one model, but not with others. This is due to the violation by the laptop manufacturer of the RS-232 data transfer standard. They do this in order to conserve battery power.
If the manufacturer of the receiver was technically scrupulous and accurate, then a special chip for the COM port will be installed in the receiver. Thanks to this chip, the receiver will work with both a laptop and a computer. But installing a microcircuit increases the total cost of the product, and lately manufacturers have been saving even on these little things! It is because of this that the problem of incompatibility between laptops and most receivers arises.
When using a computer, the problem of the lack of the necessary RS-232 ports is solved simply: you need to purchase an additional module with COM ports and. This board installed in the computer is called "PIC-COM" or simply "COM ports board". Rice. PCI_RS-232 PCI board for a computer with two COM ports.
If you are not strong in computers and have never dealt with the installation of additional equipment in a computer, then contact a specialist! Otherwise, you can "kill" expensive equipment.
After the board is installed in the computer, the operating system "Windows" - "OS" assigns a number to the newly installed ports, for example, "1" and "2".
When using a laptop, you cannot install a regular board from a computer - the standard and size are not the same. There are two ways to solve this problem: expensive, but high-quality and cheap, but not fully compatible. In the first case, you need to purchase a special board with ports for the laptop.
Rice. plata_Notebook Notebook board with COM port.
The price for these boards is extremely high, and I did not manage to purchase this board, even on order.
And there is a catch: in "old" and "new" laptops there are two standards for external boards! Before purchasing, check the instructions for your laptop!
If you could not purchase a board for a computer or laptop, then there is only one way out: “USB”.
Almost all modern computer models have a “USB” output, at least two, or even all eight! Various USB-COM converters are commercially available.
Rice. USB-COM Converter "USB-COM".
That is, the input of such a “converter” is connected to the free “USB” connector of the computer, the driver (control program) is installed from the disk from the kit, and system settings a virtual COM port appears with an assigned sequence number.
Here the first problems await us: firstly, the OS could assign too large a number to the virtual port, for example, “25”. And the program for "firmware" of the receiver allows you to work with port numbers from one to four. Secondly, not all USB-COM converters can work with the firmware program and the receiver itself - various equipment manufacturers have manufactured their products and programs for them in different ways. It is necessary to check all converters individually for your program and your receiver. It often happens that the converter works with one equipment, but not with another.
If the first problem is fixed by changing the port number in the OS settings, then the problem of compatibility of hardware, program and converter cannot be.
To change the assigned OS number, you must change it manually. To do this, you need to enter the "Device Manager": "Start" - "Settings" - "Control Panel" - "System". Rice. Panel_upravlen Launching the "Control Panel"
In the window that appears, select the "Hardware" tab and click on the "Device Manager" button. The Device Manager window will open. In the window that appears, in the tree-like list, select the line “Ports (COM and LPT). In the drop-down list, you will see all the ports available on your computer. Select your virtual port: "USB to COM converter". I have a "Prolific" model converter. Rice. port_USB-COM-1
Click on this line with the RIGHT mouse button, in the window that opens, select the “Properties” option. Rice. port_USB-COM-2. In the window that appears, select the "Port Settings" tab. In the "Speed" line, select "115200", then click on the "Advanced" button. Rice. port_USB-COM-3. At the bottom of the window that opens, find the "COM Port Number" tab. Rice. port_USB-COM-4. Click on the tab and select the desired COM port number.
Note that some port numbers may be occupied by existing equipment, such as the built-in modem. You cannot use one port at the same time!
After completing the settings, click "OK" to save changes and completely exit the settings mode by closing all previously opened windows.
After that, restart your computer to make the necessary changes. If you changed the number of the COM port of the "USB-COM" converter, then simply remove it from the computer connector and reconnect it.
About RS-232 (wiring cables, connectors, brief description)
RS-232C contacts
Wiring the "modem" RS-232C interface cable
Communication and RS-232 interface
Troubleshooting RS-232 Communications
RS-232C contacts
RS-232C interface DB-9 connector pins
Wiring the "modem" RS-232C interface cable
Wiring the Null Modem RS-232C Interface Cable
RS-232C Cable Wiring for Kramer Switches
Communication and RS-232 interface
When working in potentially noisy environments, we need a reliable means of transmitting data. The most common standard is still the archaic RS-232C (Recommended Standard 232 Version C), adopted by the Electronic Industries Association (EIA) in August 1969.
Advantages of RS-232:
Popularity - all PCs (but not Macs) are equipped with at least one RS-232 port
Ease of acquiring ready-made cables
Ability to use hardware control of the transfer process (often not used!)
Disadvantages of RS-232:
Point-to-Point Communication (DTE? DCE)
Low, by today's standards, speed (typically 9600 baud [bits per second])
Works only at short distances (up to 10 m)
The composition of the communication lines between DTE and DCE devices is not precisely defined. The standard describes the functions of up to 25 trunks, but does not specify whether a particular trunk should or should not be used. Things are better (technologically) in the RS-422 standard. According to this standard, communication is carried out over two pairs of wires, and the transmitted signal can be received by more than one device. The RS-485 standard (improved RS-422) uses a single pair of wires that is used to transmit or receive by many devices.
Features and benefits of RS-422/RS-485:
Can be used for multipoint connections
It is the de facto standard for much of the broadcast video industry!
Can be used at distances up to 1.2 km
High noise immunity due to the use of differential (balanced) communication lines
KRAMER VP-43 Range Extender:
Designed to overcome distance limitations for our RS-232 controlled products.
Converts to RS-422 and then back to RS-232, allowing two pairs of wires to be used as physical media.
Can be used to extend the communication distance for any null modem RS-232 connection.
It can also be used to control our products via RS-422, or as a converter general purpose from RS-232 to RS-422 and vice versa.
Port Extender KRAMER VP-14 Port Extender:
Designed to overcome the limitation of the RS-232 interface, which can only make point-to-point connections. Allows communication between multiple devices with RS-232 interfaces.
Data that arrives at any of the ports of the device is sent to the other 3 ports.
Can be used to control the switch from 3 DTE devices (eg computers).
Works in all communication modes (number of bits, speed, parity, etc.) and does not require setting these parameters.
Troubleshooting RS-232 Communications
The following are steps that can help resolve problems when communicating with Kramer devices via the RS-232 interface.
1. Make sure that a null modem connection is established between the device (switch, router) and the host computer (PC).
The easiest way (when using the 25-pin port on the PC) is to use the null modem adapter that came with the device. Connect such an adapter with a 25-pin connector to the serial port of the PC, then use a straight cable - that is, one-to-one soldering - connect the 9-pin connector of the adapter to the serial port on the device. (If the adapter is used with a partial cable, then at least a 9-pin connector must be connected at both ends: pin 2 to pin 2, 3 to 3 and 5 to 5.)
When directly connecting the 25-pin port on the PC to the 9-pin connector on the device (i.e. without a null modem adapter), connect the following:
Pin 2 on 25-pin connector - with pin 2 on 9-pin
Pin 3 on a 25-pin connector - with pin 3 on a 9-pin
Pin 7 on a 25-pin connector - with pin 5 on a 9-pin
Short together pins 6 and 20 on the 25-pin connector
Short together pins 4, 5 and 8 on the 25-pin connector
When directly connecting the 9-pin port on the PC to the 9-pin connector on the device, connect the following:
Pin 2 on the PC connector - with pin 3 on the device connector
Pin 3 on the PC connector - with pin 2 on the device connector
Pin 5 on the PC connector - with pin 5 on the device connector
Short together pins 4 and 6 on the PC connector
Short together pins 1, 7 and 8 on the PC connector
2. Make sure all DIP switches are set correctly on the device.
3. Make sure the baud rate settings on the PC and the device are the same, and the correct COM port is selected on the PC.
4. If multiple devices are being used at the same time, make sure they are all turned on. If any of the devices is turned off in a master/slave system, the exchange in such a system will not be reliable.
5. If the device has a "DISABLE TXD" function, make sure that this function is disabled; likewise, if a DIP switch is used to "disable answer", make sure answer is enabled.
6. Pin 3 on the RS-232 connector of the device is used to send data to the PC (this is the TXD of the device and RXD on the PC). Pin 2 on the device connector is used to receive data from the PC (this is the RXD of the device and TXD on the PC). It may be useful to use a digital storage oscilloscope to verify that the device is transmitting/receiving data on the specified pins.
7. Most devices use a "bidirectional" communication protocol. This means that the same code is used both to send a command to the device to perform a certain action, and as a response from the device (on the PC) when a button on its front panel is pressed to perform a similar action. For example, if the user pressed the buttons and switched input 4 to output 5, the device sends to the computer hex code 7B; at the same time, when the device receives code 7B, it will also work out the connection of input 4 to output 5. For such a protocol, it may be useful to analyze the codes sent by the device when pressing the buttons on its front panel in order to understand the exchange protocol.
8. When troubleshooting, it may be helpful to use a communication program like Procomm or Viewcom to first analyze the codes sent by the device. Then you can try to send such codes back (see point 7), checking that the device responds to them correctly. Finally, you can send a code by which the device will return its state.
9. If a user-written program is to be used, first check with a proprietary program, if possible, that the communication between the PC and the device is working properly.
10. For equipment that has RS-232 control as an option and is introduced by installing an optional hardware board, check that the board is properly installed (as described in the manual). Particularly for the X02 switch series, check the straight cable that connects to the module and make sure there are no jammed pins on the connectors.
11. Some devices may be controlled by other pieces of equipment and may be configured to operate via RS-232 with such equipment rather than with a computer. In this case, you must correctly configure the device. For example, models BC-2216 and BC-2616 (matrix switchers sound signals 16X16) are factory-configured (default) to work with the BC-2516 (16X16 video matrix switcher). In this case, the sound matrix receives control from the PC through the video matrix. If the sound matrix is to be controlled independently, it must be reconfigured accordingly (to operate as an audio-only device).
12. If you need to send several commands, then before sending additional command you should make sure that the device has completed the previous command. To do this, wait for a response to the previous command before sending the next one.
13. Make sure the real RS-232 interface is used to communicate with the device! Some equipment (such as the standard Macintosh serial port), although similar to RS-232, uses different communication modes.
14. When using a PC with an operating Windows system NT4.0 (and below) should take additional steps. This system does not have a "plug and play" function, and therefore setting up computer ports in it is not an easy task. See your Windows NT documentation! Even if your program is running on a computer with a different operating system, it is possible that under Windows NT the port will not initialize correctly.
15. Please note that the working distance for RS-232 (by definition) does not exceed 10 meters! If a longer link length is required, our VP-43 "link extender" should be used.
16. By definition, the RS-232 interface is designed to exchange between 2 ports (in our case, this is a PC and a switch). If you need to connect several devices with RS-232 interfaces together, you can use VP-14 (for example, if you need to control the switch from 2 computers and a BC-2000 controller).
(NOTE: For some products in our range, it is possible to control several of these devices when they are connected in series with straight cables - which seems wrong in the light of the above! In fact, we configure the devices in master / slave modes (master / slave), while only one device, the master device, is connected to the computer via RS-232.With this inclusion, the master device transmits information to and from the PC to the slave devices, and the ports are connected in pairs by the RS-232 interface.)
Installing new software in satellite receiver only possible through a null modem cable. In simple terms, this is called the firmware of the satellite receiver. For receivers equipped with an RS-232 connector, updating software, keys, removing a dump, restoring the receiver's performance in most cases is used only with a null modem cable. To connect the receiver you will need a computer or laptop with (USB-COM adapter) or COM port. Operating system you can use Windows 98, Windows XP, Windows 7 to match the computer receiver. Attention! Connect and disconnect the cable from the receiver only when it is disconnected from the 220 volt network. During a firmware update, never interrupt the software update process. All this can lead to the failure of the satellite receiver.
Briefly about the null modem cable. The scheme is simple, and guided by the photographs below, it will not be difficult to make it yourself at home. As a last resort, he will buy it on the radio market or in a computer store. To make a null modem cable with your own hands, you will need 2 RS-232 connectors (female connector type), a cable with three cores and a shield, it is very important that it be shielded, which will give stability when working with it. Do not make it too long! All this will need to be soldered according to the scheme below, guided by the photo, see below.
Diagram of a null modem cable of a satellite receiver
General form null modem cable. The total length can be up to 10 meters. It is recommended to use a shielded 3-wire cable. Solder the screen to the ground.
photo 1
Below in the photo is a null modem cable for a satellite receiver without connectors. 3 wires and a screen are involved.
photo 2
Schematic representation of a null modem cable for a receiver.
photo 3
A modern laptop or netbook does not have an RS-232 port. Only USB 2.0 or USB 3.0 Therefore, to flash the satellite receiver, you need to use an adapter like USB-RS232 (see the photo below). Such an adapter can be purchased at a computer store. It is inexpensive. The adapter comes with a CD software- driver. The driver must be installed on a laptop, netbook. Please note the USB-RS232 adapter is used together with a null modem cable. Without a null modem cable, you will not be able to flash the satellite receiver, as the connectors will not match. See above for a null modem cable diagram.
Null modem connection. From my experience.
Why else would you need such a connection? For example, a friend came to you and wants to fill you up a couple of times with a rocket launcher. Or you have two computers at home (and this is not such a rarity) and you want to have Internet access from both computers, while having one modem. Or maybe you need to transfer several large files from one computer to another.
For such a connection, it is enough to buy a so-called null-modem cable. Cables for COM and LPT ports cost about the same ($3 - $6), the data transfer rate is also about the same. The advantage of such a connection is its low cost and the absence of additional equipment. Disadvantages: small distance (up to 5 m) between computers; low speed data transmission; one-way communication control.
Who remembers DOOM1 at work or at the institute, he probably remembers the so-called "string" - 3 wires attached somehow to the COM ports of two three-ruble cards (Intel 80386). This simple device allowed you to play against each other or together against monsters, which brought into the game new element thrills. FROM advent of Windows and games requiring communication using IPX, TCP/IP pro this device forgot. But in vain. Everything is not so complicated, and for the home this is a very attractive solution, and its name is NULL-MODEM. So, there are two types of null modems: for COM (serial) ports and for LPT (parallel) ports. The first type is connected to the same type of ports as a regular modem (there are usually 2 of them), the second one is connected to the printer port (which is not very convenient if you have a printer).
Null-modem connection for COM ports is convenient because on a computer, usually, one COM port is free. The disadvantage is that the data transfer rate is only 115200 bps. Only 2-3 times faster than a good Internet connection. At this speed, 1 megabyte of data is transferred in just over a minute. In general, if you decide to use a null modem cable for COM ports, then it is better to buy it. The fact is that there are 2 types of COM ports: DB-25 (wide, 25 pins) and DB-9 (narrow, 9 pins). At the radio bazaar or at a company selling components for computers, you can purchase a universal null-modem cable. Each end has a pair of connectors - one for DB-25 and one for DB-9. If you decide to solder it yourself, then use the diagram below:
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I do not recommend trying to insert the cable into the connectors with the power on at least one of the computers: you can burn the port. Well, if you still do this, then first you need to touch the connector housing. If you connect without turning off the computer, then you still have to reboot to initialize the ports.
What else I noticed: the English Norton was on the laptop, and I had Russian, the communication programs were respectively called telnet.exe and telemax.exe. When transmitting 2 MB of information, about 300 errors were collected. When I installed the same Russian version on two machines, the number of errors dropped to zero. Don't let the inscription on the right scare you upper corner OFFLINE - and it is necessary. You can work with Norton both from DOS and under Windows. I checked only under Windows 98. True, the communication program window must be active, otherwise the speed drops dramatically and the number of errors increases, but the connection is not interrupted.
It does not matter which connectors to use: 9 and 25, 9 and 9 or 25 and 25 pins, the main thing is to specify in the Telemax program from the Norton software set that you need to use such and such a port. If the computer was turned on, then you need to reboot after connecting. For a long time I could not find Norton Commander on the Internet - I came across only non-working links. Therefore, I will lay out the Norton shell with the Telemax program for download, we will need it. I gave the view of her shell above. For the convenience of downloading and transferring on a floppy disk, I pretty much cleaned up the folder, leaving, in fact, Norton Commander and Telemax. The default settings can not be changed, but be sure to check the port where the wire is connected. I can say more - if there is no connection and not crooked hands - the port is incorrectly specified. After changing the port, you need to save the settings so that they are the next time the program is loaded. To check, run Telemax on two machines and send the file via ZModem from one. On the other, a download window opens automatically. When the download is complete, a beep will sound.
Additional Information:
Bezsmertny V.S.
admin www.shems.h1.ru
Ukraine, Kyiv
GREENCONNECT manufacturer of linking, modem and NULL modem cable COM port DB 9 RS-232.
In St. Petersburg, since 2016, the production of cast modem cable mother-mother and cable male-male COM extension cable for the modem allowed to significantly expand the range and the lineup manufactured products.
Usage modem or null modem device control cables Cisco or game consoles, terminals, point of sale terminals, various devices control by modems requires both standard and special wiring.
GREENCONNECT manufactures null modem and RS-232 COM port modem cable both with standard wiring and according to special, individual schemes. For standard wiring null modem cable uses a nine-wire cable. AT modem cable GCR-DB9CM2M also involved all 9 pr vodnikov.
High quality, shielded, stranded, soft, copper conductor allows the use GCR modem cable for both domestic and industrial purposes. factory production modem cable guarantees its performance for a long time, thanks to internal fixation using Injaction Molding technology.
Modem cable COM port models GCR-DB9CM2M are available in lengths from 50 cm to 10 meters, as well as male-female extension cable COM port model GCR-DB9CM2F.
Partnership directly with the Russian manufacturer GREENCONNECT Russia will save you a lot of money and use high-quality modem cable for your tasks.
You can order or buy null modem cable from stock in any quantity at the best price.
Please note that the wiring of the RS232 modem cable is varied (depending on technical tasks).
Wiring diagram semiduplex RS-232 cable
This circuit is used to control 2 devices that send data to the floorduplex. For example, one device is sending data and both other devices are waiting for incoming data.In half duplex mode, both devices cannot transmit at the same time. If this happened, then the data would be impossible to read. This method is used in all connection schemes.from master to receiver. In this method, the computer (P3) cannot send data and interfere with the communication between external devices.
Wiring diagram duplex RS-232 cable
This cable is used when you need to control communication between two external devices that can send async data (full duplex). You need 2 RS232 ports on your computer (separate port for communication and incoming data). A modern Serial Monitor can display both sides of full dual RS232 communication in "Dual Ports" mode. In this mode, the computer (P3, P4) cannot send data and interfere with data exchange between external devices.
