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BEGINNER’S SECTION
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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.
Serial interface of a digital receiver
16 TELE-satellite & Broadband — 06-07/2009 — www.TELE-satellite.com
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Serial Interface
Null modem cable for
connecting a receiver
to the PC
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
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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.
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