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EQ-6/Atlas handpaddle protocol (v3 - 11 Jan 2004).
Darren Hutchinson
dbh@gbdt.com.au
$Id: eq6-serial.txt,v 1.3 2004/03/07 07:44:59 dbh Exp $
Introduction:
The EQ-6/Atlas hand controller is used to control the operation of the
Atlas/EQ-6 mount. The hand controller also acts as a power switch for
the mount.
The communication bewteen the controller and the mount is
unidirectional, with data being sent from the controller to the mount
over a single wire. The other wires provide ground, +12V from the mount
to the controller, and switched 12V back to the mount.
Cable pinout TBD.
Physical format:
The signal is a 0/5V signal, with a '1' represented by 5 V. Start bits
are '0', stop bits are '1'
Data format:
The data is a set of 6 asynchronous words with a format of 1 start bit,
9 data bits, and 1 stop bit. The bits are transmitted at rate of 935
bits per second. The six words are transmitted every 76.2 ms.
Note that there is no indication in the data of which word is actually
the first in the set of words. The ordering below is a guess based on
the distribution of extra stop bits in the set of words.
The distribution of extra stop bits between the six words depends on
which keys are pressed but it seems unlikely that this is detected or
used by the mount.
The six words are divided into two sets of three, one set for RA, the
other for DEC. Each set contains a sync word, a direction word, and a
speed word.
All words below are shown with the most significant bit on the left. The
least significant bit is transmitted first, immediately after the start
bit. All RA words have bit 8 set to 0, all DEC words have bit 8 set to 1.
Word 1: RA sync
This word is always the bit pattern 001111110 (0x07e).
B0: Always 0
B1 - B6: Always 1
B7 - B8: Always 0
Word 2: RA direction
This word determines the rotation direction of the RA axis,
B0: 0 = RA left, 1 = RA right.
B1 - Bit 8: Always 0
Note: When no keys are pressed Bit 0 is 0 when the controller is set for
southern hemisphere operation, and 1 when set for northern hemisphere
operation.
Word 3: RA speed
This word determines the speed of the RA axis in multiples of the
sideral rate. There seems to be some logic in the controller for the x2
speed to help with guiding:
B3 - 0 Rate
0000 x0 (RA button for opposite direction to hemisphere RA in x2 mode)
0001 x1 (No RA button pressed)
0010 x2 (RA button for same direction to hemisphere RA in x2 mode)
0100 x8
1000 x16
B8 to B4: All 0
Word 4: DEC sync (?)
This word seems to be used to synchronize the start of the DEC
information, but it could be used for something else
B0 - B7: All 0
B9: Always '1'
Word 5: DEC direction
This word determines the direction of DEC axis rotation.
B0: 0 = DEC UP, 1 = DEC DOWN
B1 - B7: All 0
B8: Always 1
Word 6: DEC speed:
This word determines the spped of rotation of the DEC axis.
B3 - B0 Speed
0000 x0 (no motion)
0010 x2
0100 x8
1000 x16
B7 - B4: All 0
B8: Always 1
Notes:
- The DEC reverse and RA reverse seem to be inputs to the controller MCU
but only control the interpretation of the buttons and are not sent
directly to the mount.
- see eq6-mnt.txt for pinout of cable
Further work:
- Need to determine correct "first word" in set by monitoring data from
startup
- Need to check for any special startup words by monitoring data from
startup