A hybrid real-time UNIX controller for the Donner 600-crystal positron tomograph

A hybrid real-time control system for the Donner 600-crystal positron tomograph has been implemented using a UNIX host computer interfaced to CAMAC via SCSI. Coincidence logic and front-end electronics have been previously described. Low-level data acquisition is carried out in this system using eight LeCroy 3588 histogrammers, which together after derandomization, acquire events at rates up to 4 MHz, and two dedicated Motorola 6809 microprocessors, which arbitrate fine timing control during acquisition. A SUN Microsystems UNIX workstation is used for high level control. Communications between the high and low level units is carried out via a Jorway 73A SCSI-CAMAC crate controller and a serial interface. Use of the workstation allows an easily-extensible user-friendly interface in an X-windows environment, as well as real-time communication to the low-end acquisition units. In the UNIX configuration, a general purpose process serves as a message center between the user interface and the CAMAC devices. The message center transfers user-specified data acquisition protocols to the tomograph hardware. A separate high priority UNIX process is used to rapidly receive sinogram data into memory during active acquisitions. This hybrid approach allows user interface and programming simplicity at the UNIX end, while supporting rapid data transfer for dynamic positron emission tomography