Loop Controller

LC card for different architectures and buses. Handles all communications between the control computer and Group3 Device Interfaces.

The Loop Controller (LC) card has a co-processor on board that handles all communications between the control computer and Group3 Device Interfaces (DIs).

It relieves the control computer of any of the communication overhead involved in high speed communications on the fibre optic loop.

The control computer and the loop controller co-processor communicate through 2 kbyte of dual port RAM on the Loop Controller card. To send a new control value to a DI, the computer simply writes the new value into the appropriate area of the shared RAM; the processor on the LC card automatically lifts this new value and sends it out on the fibre optic loop to the DI. The LC card also continuously interrogates the DIs and updates the dual port RAM with the new status values. The computer just reads the dual port RAM to get the latest status value read back from a DI. Thus the computer is not involved directly in communication with the DIs; it simply accesses the dual port RAM, while the LC looks after all communication overhead.

There are a number of loop controllers adapted to different computers:

  • ISA bus
  • PCI bus
  • VME
  • STD
  • CAMAC

The dual port RAM structure makes it relatively easy to adapt the card to other computer architectures.

Consult your Group3 representative for the latest list of LCs available.

ISA Expansion Slot Loop Controllers

There are two loop controllers designed for a PC- ISA expansion slot on an IBM PC compatible computer:

  1. Model LC1-PC handles a single loop
  2. Model LC3-PC can service three independent loops from a single expansion slot

PCI Expansion Slot Loop Controllers

There are two loop controllers designed for a PCI expansion slot:

  1. Model LC1-PCI handles a single loop
  2. Model LC3-PCI can service three independent loops from a single PCI slot.

Loop Controllers on Other buses

  • Model LC2-VME is a VME card that can control two loops of DIs from a VME crate.
  • Model LC-STD controls a single loop of DIs from a STD bus crate.   
  • Model LC-CAM controls one or two loops of DIs from a CAMAC crate.

Other control computers

VME, CAMAC, and STD based control systems are very diverse so no general comments can really be made about control software. The Group3 hardware gathers all the information from the I/O boards on the fiber optic loop and places it in a memory that is accessible from the VME, CAMAC, or STD crate bus. The addresses at which the data is placed in memory is detailed in the Loop Controller Programmers Manual. The control system software engineer then has to write code to allow the overall control program access to this memory. Programs like VISTA and EPICS allow easy access to memory, so interfacing to similar packages usually presents litle problem.