BEGINNER’S SECTION
Receiver Connections
Data Exchange Between PC and Digital Satellite Receiver Thomas Haring
Strictly speaking, a digital receiver is nothing else than a PC in miniature. While it does, of course, prioritise different tasks and serves an entirely different purpose using different components and user interfaces, it nonetheless comes equipped with a central processing unit, various types of memory and a connection for signal output to a connected device. So what makes more sense than establishing a digital connection between a satellite receiver and a PC for exchanging data, putting out signals on additional devices and controlling the receiver via remote access? To achieve just this, three connection types have been established in the course of time, and this report will introduce you to all of them.
■ Pin configuration of a 3-strand null modem cable to the PC
as no surprise that the data transfer rate of serial interfaces is very low and does hardly exceed 0.8 Mb/s. So as far as speed is concerned, this interface is a thing of the past, even though most PCs boast at least one serial interface even up to this day. Receiver manufactures had joined this bandwagon and began to equip their receivers with a serial interface as well. Another reason for this development was that the chipsets available at the time when digital satellite television was introduced were hardly capable of supporting other connection types. And if we take into account that PVRs at that time were in experimental stages only, to say the least, and that data exchange only involved channel lists and software, then the transfer speed to be reached with a serial connection was sufficient at the time. So-called null modem cables are required for a serial connection, and they consist of either 3 or 9 strands. The 3-strand type is not capable of performing handshakes, while the 9-strand type supports this.
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Null modem cable for connecting a receiver to the PC
Serial Interface
■ Serial interface of a digital receiver
Right from the beginning of personal computers – and that is to say a long time before the advent of the digital satellite age – PCs started to feature serial interfaces which allowed users to connect and control peripherals such as a computer mouse, or to establish a connection to the outside world with the help of a modem. Given the fact that this was introduced many years ago it comes
16 TELE-satellite & Broadband — 06-07/2009 — www.TELE-satellite.com
A handshake in this case means that hardware controls the data flow and thus makes sure data can flow uninterruptedly. For simply reading and writing channel lists or for updating the receiver’s software a 3-strand null modem cable will do, as the software will emulate flow control in these applications. Null modem cables are available in PC stores or can even be DIY-ed using rather simple tools (see plugging diagram). Please do make sure, however, that the terminal plug always has nine pins, even if only three of them are wired. Any major electronics shop should have