[vdr] Re: DiSEqC for Dummies

[Ora Järvinen <vdr@oraweb.de>]

DiSEqC _can_ be extremely complex - however, in a typical "private"
installation, it not that bad.

A typical command in diseqc.conf look like this:

S19.2E  11700 V  9750  t v W15 [E0 10 38 F0] W15 t

The actual DiSEqC command is the one in square brackets. The meaning of
these four bytes is

E0 = Command from master, first transmission, no reply required
10 = address byte, the value means "All IF switching components"
38 =command byte, this value means the command describes the IF path

You normally never need to change these three bytes. The last byte
determines what actually happens. It consists of two nibbles - the upper
four bits can usually be "F" (it describes which bits are to be cleared
before the command is executed, the bits correspond to the lower nibble). In
the lower nibble, bits 2 and 3 define the input port of a DiSEqC switch (bit
2 is called the position bit, bit 3 confusingly the option bit). With the
two bits, you can (obviously) select one of 4 inputs:

F0 = 1
F4 = 2
F8 = 3
FC = 4

The DiSEqC information is sent by keying the same 22 kHz signal that is also
(usually) used to select the low/high band. The standard requires a pause of
at least 15 ms between the continuous tone and a DiSEqC message, that's why
the W15's are there.

So, if you have, say, the Astra LNB connected to input 1 of a switch, and
Hotbird to input 2, diseqc.conf should look something like this:

S19.2E  11700 V  9750  t v W15 [E0 10 38 F0] W15 t
S19.2E  99999 V 10600  t v W15 [E0 10 38 F0] W15 T
S19.2E  11700 H  9750  t V W15 [E0 10 38 F0] W15 t
S19.2E  99999 H 10600  t V W15 [E0 10 38 F0] W15 T

S13.0E  11700 V  9750  t v W15 [E0 10 38 F4] W15 t
S13.0E  99999 V 10600  t v W15 [E0 10 38 F4] W15 T
S13.0E  11700 H  9750  t V W15 [E0 10 38 F4] W15 t
S13.0E  99999 H 10600  t V W15 [E0 10 38 F4] W15 T

The whole sequence basically switches the 22 kHz tone off, selects 13/18
volts according to the polarisation, waits 15ms, sends the DiSEqC command,
waits 15 ms, and switches the (continuous) 22 kHz tone on again (if needed,
i.e. the upper band).

This should work for all normal DiSEqC switches (2/1 and 4/1) and LNBs
(single, twin, quad). For (most) 2/1 switches, the "mini A" and "mini B"
commands can be used also, but their is no real advantage here, it's mainly
for backwards compatibility. (The command sequence is a bit shorter though,
so you save a few ms).

A somewhat more complicated configuration would be using one or more
"quattro"  LNBs and a "multiswitch". A quattro LNB has four outputs and no
internal switching, so a separate multiswitch is needed. In most cases,
these switches also obey the 13/18V and 22 kHz signals, so the above
commands should work too. There are, however, switches which understand
DiSEqC for selecting lo/hi band and polarisation also. This selection is
done by the two lowest bits of the last byte in the command: Bit 0 selects
the band, bit 1 the polarisation. In this case, assuming you have two
quattro LNBs (Astra/Eutelsat) and a multiswitch with full DiSEqC
capabilities (and 8 inputs), the commands should look something like this:

S19.2E  11700 V  9750  t W15 [E0 10 38 F0]
S19.2E  99999 V 10600 t W15 [E0 10 38 F1]
S19.2E  11700 H  9750  t W15 [E0 10 38 F2]
S19.2E  99999 H 10600 t W15 [E0 10 38 F3]

S13.0E  11700 V  9750  t W15 [E0 10 38 F4]
S13.0E  99999 V 10600 t W15 [E0 10 38 F5]
S13.0E  11700 H  9750  t W15 [E0 10 38 F6]
S13.0E  99999 H 10600 t W15 [E0 10 38 F7]

Note that because everything is now controlled by DiSEqC, the tone/voltage
commands can be left out. (Actally, the "t" command is superfluous, as the
tone has never been turned on, there should be no need to turn it off). If
you're paranoid ;-) you could add "W15 t" after each command too.

Hope this helps.... ;-) sorry for the longish post.

I'll save the description for cascaded DiSEqC switches to the next post :-)

Adrian P Challinor wrote:
> Seconded! Diseqc is on my horizon and if there are any howto's or
> Gotcha guides I would like to read them.
>
>
> Adrian



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