Introducing the CAMAC interface.

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Introducing the CAMAC interface.
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• The original concept of CAMAC The CAMAC
  (Computer Automated Measurement and Control),
  standard IEEE 583-1975 was defined by the
  European StandardsOn Nuclear Electronics (ESONE)
  Committee of the Joint Research Centre (JRC)
  Ispra to permit any number of incompatible
  laboratory instruments to be interfaced with
  computers.
• The committee suggests the important
  features are-
• A modular system with functional plug-in units
  that mount in a standard crate.
• Designed to exploit the highest packing
  density possible with solid state devices???
• Plug-in modules connect to data highway
  (Dataway) that is part of the crate and carries
  data, control signals and power.
• Can connect to on-line computer although
  the use of a computer is optional.
• Crates can be connected together by either
  parallel or serial highways.

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CAMAC in astronomy a brief history Typical
applications for CAMAC in the nuclear industry
were pulse height discriminators and rate meters.
The HEGRA cosmic ray observatory on La Palma used
CAMAC modules in this application.InstrumentsRG
O and other astronomical observatories such as
AAO and NOT use CAMAC as a convenient means to
interface instruments, telescopes and detectors
to control computers.Several early RGO La Palma
and AAO instruments were controlled through CAMAC
using Perkin Elmer computers such as Peoples
Photometer and QUBES, but by the late 80s RGO had
shifted to an in house control systems programmed
in FORTH designated as the MMS and 4MS instrument
controllers. Since mid 90s new WHT instruments
have been controlled by EPICS, these have some
similarities to CAMAC but use an in crate
processor.TelescopesCAMAC was retained for
telescope control and has continued after the
change over from Perkin Elmer TCS (INT and JKT)
and MicroVax TCS (WHT) to Alpha workstations.
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CAMAC usage in ING Telescope Systems

• External
• Parallel input absolute encoders, switch closures
  (limit switches), time service
• Parallel output rate demand (WHT only), some
  indicator lights
• Serial input/output RS232 communication (Sony
  Transducer!)
• UP/Down counters incremental encoders
• Analogue to digital converters truss/mirror
  temperature, displacement
• Transducers
• Digital to Analogue converters rate demand (INT
  and JKT)
• System
• Branch extenders Needed when extra crates are
  added
• Crate controller Required to control crate and as
  a link to other crates
• Branch terminator Always required in the final
  crate
• Clock buffer Not really a true CAMAC used for
  clock fan out
• Diagnostic Word generators, Dataway Test Modules

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CAMAC Basics (Node addresses)

• CAMAC addresses are node (niche) specific they
  dont therefore
• have DIL switches that select a particular
  address, the
• programmer must specify a slot when addressing a
• module.

Node 8
Crate 0 The system crate by definition
2 6 8 10 12 16
Node 12
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CAMAC Basics (Connecting crates)
Computer with CAMAC driver loaded
CAMAC interface plugged into computer PCI bus
Branch extender module
Branch 0 Crate 0
Computer interface module (computer specific)
Branch 6 Crate 1
Branch 6
Branch 6 Crate 2
Branch 6 Crate 3
Crate controller modules
Branch terminator module
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CAMAC Basics addressing a module

• Branch (only single branches at ING always 0 or
  6)
• Crate (crate addresses range from 0 to 3 at ING
  the maximum possible is 7)
• Node (or Niche!) 25 stations or nodes are
  available in an a standard CAMAC crate, the
  rightmost, station 25 is reserved for a crate
  controller, addressed modules may be plugged into
  stations 1 24
• Subaddress used for addressing registers in
  inside modules, 4 bits are available giving 16
  possible subaddresses.
• Function used for controlling the available
  functions within a module, 5 bits are available
  giving 32 possible functions for diagnostic
  purposes F 0 read and F 16 write are worth
  remembering.

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CAMAC Basics B C N A F

• To communicate with a particular CAMAC module a 4
  word address and a 5 bit function code must be
  specified. The TCS programme reads or writes to
  most modules at 20Hz. A diagnostic programme is
  available on the Alpha TCS computer (CAMTEST) for
  either writing to or examining the contents of
  module registers
• Familiarity with the use of CAMTEST is essential
  for duty engineers apart from the PLOT program it
  is the most important tool you have for tackling
  telescope problems
• Remember- Branch Crate Node Address Function

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CAMAC bus architecture
Command controls Z, I, C
6 volt 25amp
Read R1 R24
Write W1 W24
24 volt
Module
Crate Controller
-24 volt
Timing strobes S1 S2
-6 volt 25amp
Command Lines F1 F5 A1 A4
LAM
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Modules you should know about!RGO 32 bit counter

• Used for reading telescope position from
  incremental encoders

6 of these modules are used in the INT
(illustration) and 8 on the WHT. These 32 bit
counters accumulate counts from the telescopes
incremental encoders and transfer the
instantaneous count to a parallel register on
receipt of a pulse on the clock input.
Clock inputs
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32 bit counter architecture (greatly simplified!)
X32
Up Down



To CAMAC bus


A quad B inputs
A

B
CLOCK 20 Hz
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Things to check on the 32 bit counter

1. Are the lights incrementing or decrementing as
   the telescope axis moves?
2. Is the module being accessed by the system
   (Caution these LED are occasionally faulty).
3. Using CAMTEST check all 32 bits actually change
   state, you need to see each one in a 0 or 1
   state, this will involve moving the telescope
   over its entire angular range.
4. If you replace a 32 bit counter module ensure the
   jumper connections are identical to the module
   you removed. (Caution the up/down A quad B links
   are identified in the wrong sense on these
   modules)
5. To localise the fault try connecting the input
   from another encoder and checking if the numbers
   change on the encoder page ONLY do this test in
   engineering never in computer mode.

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Location of incorrectly labelled LK8 but just
copy links on the module removed
Access LED
32 LEDs
Clock input
Encoder input (line driven)
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Modules you should know about!450-4 Parallel
Register

• Used to read parallel data such as absolute
  encoder inputs

Note the air gaps, this resulted in a major
improvement in reliability
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Things to check on 450-4 modules

• 1.Has the fuse blown? Particularly if the module
  has been running hot as when a fan fails or the
  air conditioning is off.
• 2. Is the module being accessed by the system
• 3.Using CAMTEST are all the bits able to change
  from 0 to 1
• 4. Is the module really the problem? Blown
  encoder bulbs and failed line drivers chips and
  power supplies all show similar symptoms.
• 5. These are not used in closed loop situations
  so you could try inputting data from another axis
  to help localise the fault.
• 6. Unless it is for the focus encoder dont mess
  around at night just zeroset and fix it in the
  morning.

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OR/48 Output Register
Used to write instantaneous velocity to telescope
axes and rotators
This is the actual word being written to the
Marconi rate generator for azimuth in this
particular case 000000000000000011010101 slow!
You could test this module by writing a 24 bit
word to its CAMAC address and checking the
lights. In principle the telescope could be made
to move but in practice it is necessary to set
other bits to enable telescope movement but it
can be done.
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How to find out what each CAMAC module does

• Each CAMAC crate has a schedule attached to the
  cabinet door, some nodes have labels but your
  best reference by far is the fabulous John Mills
  PDF document available at
• http//www.ing.iac.es/eng/electronics/wht/telesco
  pe/wht_camac.pdf
• This document not only gives the CAMAC addresses
  but also describes the function of each bit. By
  reading and writing the correct bit pattern to
  CAMAC modules it is possible to make the
  telescope and dome move at any speed and
  direction you wish providing the CAMAC system
  modules are working correctly?
• Faults on branch extenders, couplers and
  terminators as well as CAMAC back plane faults
  can cause very odd behaviour. Experience has
  shown that CAMAC modules are frequently damaged
  during electrical storms even when there is no
  evidence indicating a ground strike close to the
  buildings.

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Electrical storm damage
Electrical storms (thunder storms) are less
common on La Palma than in Northern Europe,
mostly they occur in the winter and are sometimes
accompanied by falls of snow or soft hail (snow
grains). If you see lightning at a distance or
hear thunder whilst on site then you should
anticipate CAMAC problems. Circuits with long
cables such as encoders are generally the first
victims but faults extend to crate controller
modules that are inherently difficult to
diagnose. I am not aware of any preventive
action to take but a good policy is to check the
system early following the storm and have CAMAC
cognizant staff available on site despite the
snow. On two occasions I remember horrific CAMAC
carnage resulting from electrical storms!
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CAMTEST demonstration

• Using a LAT session log onto the TCS with
  username ltengineergt and password lt?gt you will be
  presented with several options but choose
  CAMTEST. On the command line type the number of
  the Branch Crate Node Address Function, on
  hitting return the program will present you with
  the contents of the register (if it is a read
  operation F0) in hexadecimal format.
• There is reasonable online help (type help) with
  examples but I find the ltRADIXgt command
  particularly useful since RADIX bin will present
  the 24 bit word in binary format making it easier
  to look for missing bits.

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Switch to CAMTEST demonstration
Reading from B0 C0 N10 A0 (time service)
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CAMTEST demonstration
Controlling WHT dome rotation
EXEC 6 3 2 1 16 1535 Move dome CW at full speed
(hex 5FF) EXEC 6 3 2 1 16 1047 Move dome CCW at
half speed (hex 57F)
Motor run bit 1
CW rotation set
All 8 bits of speed flat out!