CAMAC

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Computer Automated Measurement And Control (CAMAC) is a standard bus for Data acquisition and control used in nuclear and particle physics experiments and in industry. The bus allows data exchange between plug-in modules (up to 24 in a single crate) and a crate controller, which then interfaces to PC or to a VME-CAMAC interface.

The standard defines the mechanical, electrical and logic of a parallel bus (dataway) for the plug-in modules. Several standards have been defined for multiple crate systems including the Parallel Branch Highway definition and Serial Highway definition. Vendor specific Host/Crate interfaces have also been built.

The CAMAC standard encompasses IEEE standards:

583 The base standard
683 Block transfer specifications (Q-stop and Q-scan)
596 Parallel Branch Highway systems
595 Serial highway system
726 Real-time Basic for CAMAC
675 Auxiliary crate controller specification/support
758 FORTRAN subroutines for CAMAC.

Within the dataway, modules are addressed by slot (Geographical addressing). The left most 22 slots are available for application modules while the right most two slots are dedicated to a crate controller. Within a slot the standard defines 16 subaddresses (0-15). A slot commanded by the controller with one of 32 function codes (0-31). Of these function codes, 0-7 are read functions and will transfer data to the controller from the addressed module, while 16-23 are write function codes which will transfer data from the controller to the module.

In addition to functions that address the module, the following global functions are defined:

I - Crate inhibit
Z - Crate zero.
C - Crate clear.

The original standard was capable of one 24 bit data transfer every microsecond. Later a revision to the standard was released to support short cycles which allow a transfer every 450ns. A follow on upwardly compatible standard Fast CAMAC allows the crate cycle time to be tuned to the capabilities of the modules in each slot.