CompuScope SDK Manua.. - Egmont Instruments

On-Board MemoryOrganization of theCompuScope CardsThe A/D speeds at which CompuScope cards produce digital data can be too fast for the IBM PC bus. Themaximum transfer rate for the PCI bus is approximately 120 Mbytes/second while the maximum transferrate for the ISA bus is approximately 1.5 Mbytes/second. Consequently, all the CompuScope boards havehigh-speed on-board memory to store the digital data. The PC only accesses this data after the acquisitionis over.A/D Data StorageData from the CompuScope A/D converters are stored in on-board Static Memory (SRAM), which isconfigured as a circular buffer. A circular buffer is used to allow capture of data before a trigger event isdetected.The sequence of events that occur during a CompuScope data capture is as follows. This is list of low-levelsteps given purely for illustrative purposes. CompuScope users implement high-level driver subroutinecalls, which typically execute several low-level steps at once.—The PC’s CPU tells the CompuScope to GET DATA using the Get Data bit.—The BUSY flag is set by the CompuScope so that the PCI bus is denied any further access to the onboardmemory.—The on-board memory counters are initialized to ZERO by software and start counting up, therebystarting data storage at memory address ZERO.—The system waits for a trigger event to occur while it is storing data in the on-board memory. These dataare called Pre-Trigger data.—When the trigger event occurs, the on-board memory counter value is stored as the trigger address.—Once the trigger event occurs, a specified number of Post Trigger points are captured. The number ofPost Trigger Points were previously specified by writing to the registers on the CompuScope.—After capturing and storing the specified number of Post Trigger Points, acquisition is terminated. TheBUSY flag is then reset and the PCI bus is allowed to access the on-board memory.A graphical representation of the above sequence is shown below:Page 14CompuScope SDK Manual