Zero modem. Null modem cable for satellite receiver
About RS-232 (unsoldering of cables, connectors, brief description)
RS-232C contacts
Wiring out the “modem” cable for the RS-232C interface
Communication and RS-232 interface
Troubleshooting RS-232 Communications
RS-232C contacts
Contacts of the DB-9 connector of the RS-232C interface
Wiring out the “modem” cable for the RS-232C interface
Wiring out a "null modem" cable for the RS-232C interface
RS-232C cable wiring for Kramer switches
Communication and RS-232 interface
When working in potentially noisy environments, we need reliable means of transmitting data. The most common standard is still the archaic RS-232C (Recommended Standard 232 Version C), adopted by the EIA (Electronic Industries Association) in August 1969.
Advantages of RS-232:
Popular - all PC computers (but not Macs) are equipped with at least one RS-232 port
Ease of purchasing ready-made cables
Possibility of using hardware control of the transfer process (often not used!)
Disadvantages of RS-232:
Point-to-point communications (DTE? DCE)
Low speed by modern standards (usually 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 trunk lines, but does not specify whether a particular line 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 (Enhanced RS-422) standard uses a single pair of wires that is used for transmission or reception by many devices.
RS-422/RS-485 Features and Benefits:
Can be used for multipoint connections
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
Communication line extender KRAMER VP-43 Range Extender:
Designed to overcome the distance limitations of our RS-232 controlled products.
Converts to the RS-422 interface, and then back to RS-232, which allows you to use two pairs of wires as a physical medium.
Can be used to extend communication distance for any RS-232 null modem connection.
It can also be used to control our products via RS-422, or as a general purpose converter from RS-232 to RS-422 and vice versa.
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 device ports is forwarded 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 configuration of these parameters.
Troubleshooting RS-232 Communications
The following steps may help resolve problems encountered 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 control computer (PC).
The easiest way (when using a 25-pin port on a PC) is to use the null modem adapter included 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, with one-to-one wiring - connect the 9-pin connector of the adapter to the serial port on the device. (If the adapter is used with a partial cable, a minimum of 9-pin connectors 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 a 25-pin connector - with pin 2 on a 9-pin connector
Pin 3 on a 25-pin connector - with pin 3 on a 9-pin connector
Pin 7 on a 25-pin connector - with pin 5 on a 9-pin connector
Short together pins 6 and 20 on the 25-pin connector
Short pins 4, 5 and 8 together 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 on the device are set correctly.
3. Make sure that the settings for the data transfer speed on the PC and on the device match, 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 are turned off in a master/slave system, communication in such a system will not be reliable.
5. If your device has a "DISABLE TXD" feature, make sure this feature is disabled; Likewise, if a DIP switch is used to “disable reply”, ensure that reply is enabled.
6. Pin 3 on the RS-232 connector of the device is used to send data to the PC (this is TXD of the device and RXD to the PC). Pin 2 on the device connector is used to receive data from the PC (these are RXD devices 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 (in the PC) when you press a button on its front panel to perform a similar action. For example, if the user pressed the buttons and switched input 4 to output 5, the device sends the hexadecimal code 7B to the computer; 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 communication protocol.
8. When troubleshooting, it may be helpful to use a communications program like Procomm or Viewcom to first analyze the codes the device is sending. Then you can try sending such codes back (see point 7), checking that the device responds to them correctly. Finally, you can send a code that will return the device to its state.
9. If a user-written program is to be used, if possible, first verify that communication between the PC and the device is working properly using a proprietary program.
10. For equipment where RS-232 control is an option and is enabled by installing an additional hardware board, ensure that the board is installed correctly (as described in the manual). In particular, for the X02 series of switches, check the straight cable connected to the module and make sure that there are no jammed pins on the connectors.
11. Some devices may receive control from other pieces of equipment and may be configured to operate via RS-232 with that equipment rather than with a computer. In this case, you must configure the device correctly. For example, the BC-2216 and BC-2616 (16X16 Audio Matrix Switchers) 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 should be reconfigured accordingly (to operate as an audio-only switching device).
12. If you need to send several commands, then before sending an additional command you should make sure that the device has processed the previous command. To do this, wait until the previous command receives a response before sending the next one.
13. Make sure that you are using a real RS-232 interface 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 the Windows NT4.0 (or lower) operating system, additional measures should be taken. This system is not plug and play and therefore setting up the computer ports on it is not an easy task. Please refer to 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 operating distance for RS-232 (by definition) does not exceed 10 meters! If longer communication length is required, our VP-43 "Link Extender" should be used.
16. By definition, the RS-232 interface is intended for communication between 2 ports (in our case, a PC and a switch). If you need to connect together several devices with RS-232 interfaces, you can use VP-14 (for example, if the switch needs to be controlled from 2 computers and a BC-2000 controller).
(NOTE: Some of our products allow you to control more than one of these devices by daisy-chaining them with straight cables - which seems wrong in light of the above! In fact, we configure the devices in master/slave modes, with Only one master device is connected to the computer via RS-232. With this connection, the master device transmits information to and from the PC to the slave devices, and the RS-232 ports are connected in pairs.)
Installing new software into the satellite receiver is only possible via a null modem cable. In simple terms, this is called firmware for a satellite receiver. For receivers equipped with an RS-232 connector, updating software, keys, taking a dump, restoring the functionality of the receiver in most cases is only possible using a null modem cable. To connect the receiver you will need a computer or laptop with a (USB-COM adapter) or a COM port. The operating system for matching the computer receiver can be Windows 98, Windows XP, Windows 7. 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 failure of the satellite receiver.
Briefly about the null modem cable. The scheme is simple, and based on the photographs below it will not be difficult to make it yourself at home. As a last resort, he will buy it at 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 screen, it is very important that it is shielded, which will give stability when working with it. Don't do it too long either! All this will need to be soldered according to the diagram below, guided by the photo, see below.
Diagram of a null modem cable for a satellite receiver
General view of a null modem cable. The total length can be up to 10 meters. It is recommended to use shielded 3-wire wire. 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 the 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 firmware, you need to use a USB-RS232 adapter (see photo below). This adapter can be purchased at a computer store. It's inexpensive. The adapter comes with a driver software disc. The driver must be installed on a laptop or netbook. Please note that the USB-RS232 adapter is used in conjunction with a null modem cable. Without a null modem cable, you will not be able to flash the satellite receiver, since the connectors will not match. See the diagram of the null modem cable above.
We periodically release updates to the software of our equipment, fix errors in it, and also improve performance or add some new functions.
In order to update the device's firmware, you first need to download it to a personal computer, and then connect the receiver to the PC and restart the program. A null modem cable is used to connect the computer to the satellite signal receiver. If you do not have such an interface, you can purchase it at computer stores, although these products are not always available there. In any case, you have a choice: look for a ready-made solution or make a null modem cable yourself. The latter option will be much cheaper.
How to make a null modem
To make it, we need a four-core cable (the length is determined by the user) and two RS 232 connectors (“female”). These connectors can be found in any radio store; they are very popular, as they are present in almost every personal computer as a COM port. It can serve as a cable. To do this, we twist each of the cores together and get four conductors. Next, you need to unsolder the connectors. In this case, it is necessary to prevent accidental short circuiting, as this will lead to equipment failure. Such a null modem cable will work stably with a wire length of up to 50 meters.
This instruction is not mandatory, but it has been tested in practice:
2. Connecting the connector housings is necessary to relieve tension, since the housing touches the device. Otherwise, there is a risk of burning out the COM interface on the computer or receiver. This connection is not necessary if all equipment is grounded.
3. Preferable to use as it works better.
4. All signals use only three contacts.
5. Some receiving devices do not have a MAX232 chip (it is assumed that it will be located in an external adapter). In such devices, four pins are used on the COM port of the receiver, but the output of the adapter uses the same three pins. Therefore, before connecting a null modem cable, you need to study the documentation for your device in detail; you may first need to connect an adapter.
6. In some tuners, pins 2 and 3 on the connector are swapped. In this case, you will need a straight cable, not a crossover cable. In order to determine what type of connector is on your receiver, you should study the documentation for it.
Wiring a null modem cable RS232
In the COM interface, only three contacts and the connector body should be soldered. In such a cable it is necessary to use pins 2, 3 and 5. In the direct version of the null modem cable, these contacts are soldered equally in both connectors, and in the cross connector 2 and 3 they are swapped.
Manufacturers of satellite tuners (receivers) are constantly improving their software. At the same time, they correct errors, improve image and sound quality, and add new functions to the menu. And to update the firmware in the tuner (receiver), you need to use a computer and a zero modem to replace the old software in the tuner’s flash memory with new one.
Updating your receiver with new software is possible via a zero modem cable, which is not difficult to make yourself at home. In popular parlance, this is called firmware for a satellite tuner. For tuners equipped with an rs-232 connector, updating software, keys, taking a full dump, restoring the tuner's functionality. In most cases it is used only with a null modem cable. To connect the receiver, you will need a computer with a com port, or a laptop with a usb-com adapter. The operating system used to match the computer and the satellite tuner is windows 98, windows xp, windows 7 x32/x64 bit or higher.
Be careful! Connect and disconnect the rs-232 cable from the receiver only when it is disconnected from the 220 volt alternating voltage network. During a firmware update, never interrupt the software update process. All this can lead to failure of the flash memory of the satellite receiver.
Let's return to the null modem cable. The scheme is very simple. Everything is shown in great detail in the photographs. When making a null modem cable, you will need 2 rs-232 connectors (female connector type) - the cost is low. Sold at any computer store. A cable with three cores and preferably with a screen. You can use twisted pair cable UTP category 5e. It is very important that the cable is shielded, this will provide stability when working with it. All this can be assembled and soldered using the photographs on our website.
Below in the photo is a null modem cable for a satellite receiver with soldered connectors. 3 wires and a screen are involved.
