Orela Data Acquisition into Greater than 105 Channels through a Priority Multiplexer Operating on a Direct Memory Access and a Program Controlled Device Interface

The Oak Ridge Electron Linear Accelerator (ORELA) facility includes a linear accelerator and a series of computers for real-time data acquisition and on-line analysis of the acquired data. The unique features of the data acquisition computers are the following: a word-addressed, fixed-head disk; a direct-memory access, four-channel priority multiplexer capable of a peak data rate of 25,000 events/sec per channel; and a program-controlled, subaddressed device interface. Operation of the word-addressed, fixed-head disk through software and hardware control allows the experimental events to determine which channels are to have their contents read into the core memory from the disk for updating, with a resulting theoretical maximnum average data rate of 11,000 events/sec. Trade-offs for future systems are possible between the hardware and software. Operation of the priority multiplexer is described briefly. A modified, TMC, 4096-channel time-of-flight analyzer allows control from the computer through the multiplexer. A pulse generating unit, mounted in a triple-width NIM module, operates through one channel of the program-controlled device interface to control a TMC time-of-flight analyzer and a sample changer. The sample changer operates in a feedback loop that is controlled by a computer program.