[vdr] Re: [linux-dvb] OT: Diseqc Spec

[Sergei Haller <Sergei.Haller@math.uni-giessen.de>]

On Sun, 18 Jan 2004, Holger Waechtler (HW) wrote:

HW>
HW> are you sure it's actually used anywhere? the DiSEqC spec is ermmh -
HW> let's say somewhat fuzzy about some thing, I could well imagine that
HW> they never finished specifying this command...

why don't you use commands 6A and 6B. they are mandatory for any
DiSEqC-1.2 equipment while 6E id not.

HW> anyway - that's what I found:
HW>
HW> http://www.eutelsat.com/satellites/pdf/Diseqc/associated%20docs/position_app_note_v1.pdf
HW> (page 11)
HW>
HW> "The high nibble of the first data byte indicates how the remainder of
HW> the angular data is to be interpreted. The values  F ,  0  and  1  are
HW> allocated to support full rotation in a horizontal plane (e.g. for
HW> terrestrial sources). The nibble  0  references the angle defined in the
HW> remainder of the data to North (0°),  1  adds 256° clockwise to the
HW> angle and  F  subtracts 256°. The low nibble of the first data byte
HW> indicates the clockwise rotation angle in increments of 16°. Thus a
HW> first data byte of  00  defines due North,  01  defines an azimuth of
HW> 16° East,  0A  (hexadecimal) an azimuth of 160°, and  10  (hexadecimal)
HW> a rotation of 256° clockwise from north. The high nibble of the second
HW> data byte defines the angle in degrees, and the low nibble indicates the
HW> fractional part of a degree, if required. Note that the low nibble is a
HW> true binary fraction, and is not Binary Coded Decimal. Thus the most
HW> significant bit (of the low nibble) defines half a degree, the next bit
HW> a quarter degree and the least significant bit a sixteenth. If the
HW> Tuner-receiver User-interface is to show a decimal value, then the ten
HW> closest fractional values can be employed, as given in the following table."

was just reading the same...

basically it's what you want: the command looks like

6E PQ RS (where P,Q,R and S are 4-bit numbers, i.e., nibbles)

I suppose, you can ignore S for the moment -- it specifies the fractionals
of one degree:
 0001  1/16 of a degree
 0010  1/8  of a degree
 0100  1/4  of a degree
 1000  1/2  of a degree
and so forth, i.e.
 1110  1/2 + 1/4 + 1/8 = 7/8 of a degree


R is a number of degrees (i.e. between 0 and 15)
Q is a multiple of 16 degrees (i.e. between 0*16 and 15*16)
P can be one of 0 (exact north), 1 (+256 degrees) and F (-256 degrees)
  BTW: + means "east" and
       - means "west"

so if you want to have a position of, say, 11 degrees east, just use

  6E 00 B0 (i.e. north + 0*16 + 11 + 0 = +11 degrees)

a few more examples:

  6E 04 10 ( north +  4*16 +  1 + 0 = +65 degrees)
  6E 1D F1 ( +256  + 13*16 + 15 + 1/16 = +479.0625 = +119.0625 degrees)
  6E F1 5A ( -256  +  1*16 +  5 + 1/2 + 1/8 = -234.375 = +125.625 degrees)



c ya
        Sergei
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