Presentation on theme: "Introducing the CAMAC interface.. The original concept of CAMAC The CAMAC (Computer Automated Measurement and Control), standard IEEE 583-1975 was defined."— Presentation transcript:
Introducing the CAMAC interface.
The original concept of CAMAC The CAMAC (Computer Automated Measurement and Control), standard IEEE was defined by the European Standards On 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.
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. Instruments RGO 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. Telescopes CAMAC 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.
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
CAMAC Basics (Node addresses) CAMAC addresses are node (niche) specific they don’t therefore have DIL switches that select a particular address, the programmer must specify a slot when addressing a module Crate 0 The system crate by definition Node 8 Node 12
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.
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
CAMAC bus architecture Crate Controller Module Read R1 – R24 Write W1 – W24 Timing strobes S1 – S2 Command controls Z, I, C Command Lines F1 – F5 & A1 –A4 LAM +24 volt -24 volt +6 volt 25amp -6 volt 25amp
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 telescope’s incremental encoders and transfer the instantaneous count to a parallel register on receipt of a pulse on the ‘clock’ input. Clock inputs
32 bit counter architecture (greatly simplified!) & & & & & & Up Down A quad B inputs A B CLOCK 20 Hz To CAMAC bus X32
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 it’s 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.
Clock input Encoder input (line driven) Location of incorrectly labelled LK8 but just copy links on the module removed 32 LEDs Access LED
Used to read parallel data such as absolute encoder inputs Modules you should know about! Parallel Register Note the air gaps, this resulted in a major improvement in reliability
Things to check on 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 don’t mess around at night just zeroset and fix it in the morning.
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 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.
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 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.
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!
CAMTEST demonstration Using a LAT session log onto the TCS with username and password 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 command particularly useful since RADIX bin will present the 24 bit word in binary format making it easier to look for missing bits.
Switch to CAMTEST demonstration Reading from B0 C0 N10 A0 (time service)
CAMTEST demonstration Controlling WHT dome rotation EXEC Move dome CW at full speed (hex 5FF) EXEC Move dome CCW at half speed (hex 57F) Motor run bit 1 CW rotation setAll 8 bits of speed flat out!