Zero modem cable for USB wiring. Null modem cable for satellite receiver

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 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.

Null modem connection. From my experience.

Why else might such a connection be needed? For example, a friend comes to you and wants to shoot you down a couple of times with a rocket launcher. Or you have two computers at home (and this is not so uncommon) and you want to have access to the Internet 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 approximately the same ($3 - $6), and the data transfer speed is also approximately 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 data transfer speed; one-way control of data exchange.

Anyone who remembers DOOM1 at work or at the institute probably remembers the so-called “cord” - 3 wires somehow attached to the COM ports of two three-ruble notebooks (Intel 80386). This simple device made it possible to play against each other or together against monsters, which introduced a new element of thrill into the game. With the advent of Windows and games that require communication using IPX and TCP/IP protocols, this device was forgotten. 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, null modems come in two types: for COM (serial) ports and for LPT (parallel) ports. The first type connects to the same type of ports as a regular modem (usually there are 2 of them), the second to the printer port (which is not very convenient if you have a printer).

A 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. Actually, 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). You can purchase a universal null modem cable at a radio market or at a company that sells computer components. At each end there are 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:

I do not recommend trying to insert the cable into the connectors while the power is on at least one of the computers: you can burn the port. Well, if you do this, then first you need to touch the connector with the housing. If you connect without turning off the computer, you will still have to reboot to initialize the ports.

What else I noticed: the laptop had English Norton, and I had Russian, the communication programs were respectively called telnet.exe and telemax.exe. When transferring 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 in the upper right corner of OFFLINE scare you - that's how it should be. You can work with Norton both from DOS and under Windows. I tested only under Windows 98. True, the communication program window must be active, otherwise the speed drops significantly and the number of errors increases, but the connection is not interrupted.

It doesn’t matter which connectors to use: 9 and 25, 9 and 9, or 25 and 25 pins, the main thing is to indicate 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, you need to reboot after connecting. For a long time I could not find Norton Commander on the Internet - I only came across broken links. Therefore, I will post the Norton shell with the Telemax program for download, we will need it. I gave a view of its shell above. For ease of downloading and transferring to a floppy disk, I pretty much cleaned up the folder, leaving only Norton Commander and Telemax. The default settings can not be changed, but you definitely need 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 indicated incorrectly. After changing the port, you need to save the settings so that they will be there the next time you load the program. To check, run it on two Telemax machines and send the file via ZModem from one. On the other, a download window automatically opens. A beep will sound when loading is complete.

Additional information:

Bezsmertny V.S.
admin www.shems.h1.ru
Ukraine, Kyiv

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.

DE-9 to DE-9, DE-9 to DE-25 cables. Use this cable to connect two devices equipped with serial RS-232 interface. This cable may be used to connect any RS-232 equipped device to computer, connect two computers via COM serial port and so on. RS232 cable colors included.

The purpose of a null-modem serial cable is to permit two devices to communicate with each other without modems or other communication devices between them. To achieve this, the most obvious connection is that the TxD signal of one device must be connected to the RxD input of the other device (and vice versa).

RS-232 serial cable (Null modem) DE-9 to DE-9 with handshake

Some devices use others for flow control. One of the most common schemes is for the DTE (the PC) to assert the RTS signal if it is ready to send data, and DCE (the modem) to assert CTS when it is able to receive data. By connecting the RTS pin of one device to the CTS pin of the other device, we can simulate this handshake.

Also, it is common convention for many devices to assert the DTR signal when they are powered on, and for many DCE devices to assert the DSR signal when they are powered on, and to assert the CD signal when they are connected. By connecting the DTR signal of one DTE to both the CD and DSR inputs of the other DTE (and vice versa), we are able to trick each DTE into thinking that it is connected to a DCE that is powered up and online. As a general rule, the Ring Indicate (RI) signal is not passed through a null-modem connection.

RS-232 serial cable (Null modem) DE-9 to DE-9 without handshake

*There is no standard color scheme.

Null modem DSUB9 to DSUB25 cable

Null modem DSUB25 to DSUB25 cable

Note: DSR & CD are jumpered to fool the programs to think that they are online

A null modem cable is a very necessary thing in the satellite industry. Primarily for flashing satellite receivers. But you can’t always buy it, so you have to make it yourself.

As I already said 0-modem cable It will be useful to us primarily for flashing the firmware of satellite receivers. And if for this you can use a short one, which is easier to buy, then for cardsharing through a computer you almost always need a long or very long one (I’ve done it up to 15 m). And it’s better to solder this one yourself. And it is done quite easily.

How to do it yourself null modem cable (RS232) cord for do-it-yourself tuner firmware?

We will need two DB-9F connectors, a soldering iron, solder, a twisted pair cable, which for me is just right (you can also use another telephone you have on hand), circuits and skillful hands.

There are several connection options, but most often you need a three-pin cable. Well, if this doesn’t work, then we make a complete one for all contacts in accordance with the figures below.

A non-zero modem cable is almost always suitable. But he also has variations when his contacts go

Contacts 2 – 2 and 3 – 3, 5 -5 direct

Contacts 2 – 3 and 3 – 2, 5 – 5 not direct

It is the latter, indirect, that is most often suitable.

The wiring of the rs-232 com port in satellite receivers can look like both “father” and “mother”.

“Mothers” are much more common, so I advise you to do it with two “mothers” at the ends.

Precisely indirect null modem cable with two mothers, and with a right-to-left calculation, suitable for flashing the firmware of most satellite receivers, or for sharing.