Real-time measurement
Data Acquisition System
on IBM-PC and ECB-subcomputer basis
for use in radio-frequency & optical spectroscopy
Diploma thesis: Dipl.-Phys. Thomas Fabula from Bad Godesberg
Institute of Applied Physics, University of Bonn (1987)
“Spectroscopy, i.e. the study of emission and absorption of electromagnetic radiation by matter, is the main source of our information about atomic structure.”
Experimental setup
Setup of the hyperfine structure laser experiment in atomic spectroscopy.
Features
(i) Coupling of two computer industry standards:
(ii) Relief of the host computer from time-critical ‘on-line’ data acquisition by an intelligent subsystem
(iii) Timing asynchronous computer coupling of host and subsystem via 16-bit IN / 8-bit OUT hardware FIFOs
(iv) Highspeed I/O bus (IOB) with the possibility of connecting of up to 256 measuring modules
(v) Arbitrary expandability on all hardware levels:
- host system: PC bus compatible interface cards
- Subsystem: ECB-Bus processor/interface cards
- I/O system: fixed, standardized bus interface
(vi) Widely available software languages,
- software tools & utilities and a resulting optimal software
- development environment for both time-critical machine-oriented
- as well as time-intensive high-level language programming problems.
Description of the individual components
Host computer system
The IBM-PC compatible computer as host system is the core of the DAS, i.e. Data Acquisition System.
Due to its high computing speed (8 MHz clocked CPU), large memory capacity (640 KB RAM / 120 ns) as well as increased accuracy (8087/8 MHz coprocessor), the host system with its mass storage (10 MB hard disk, 1.2 MB and 360 KB floppy disks), it represents an ideal control and evaluation system.
The control of the experiment sequence can be realized by the program running in the subsystem and the corresponding parameter transfer via Personal Computer (PC).
A temporally asynchronous computer coupling of host and subsystem, realized by hardware FIFOs, guarantees a faultless function of the function of the PC computer at DOS operating system level. The PC-I/O board includes a 96 bit wide parallel I/O strip (4 x 8255 PPI) and two 16 bit (8254, 10 MHz) timers, bidirectional line drivers and receivers. to ensure an interference-free signal transmission between host and subcomputer.
A pre-reduction of the data as well as a graphical evaluation can be performed ‘on-line’ on the PC computer if required. The spectra can be displayed in a high-resolution (720 x 348 pixels) graphic on the screen and, if required, printed on an HP 7475A plotter or EPSON FX-100 printer.
For further evaluations, which require more time-intensive algorithms, the data can be transferred by means of diskette data carriers (5 1/4″, 360 KB) to an IBM-4381 or IBM-3081 mainframe in the local computer data center RHRZ, i.e. Rheinisches Hochschul-Rechenzentrum.
Subcomputer System
The Z80-ECB subcomputer, from Janich & Klass, controls the experiment in real time, while the IBM-PC with its comfortable operating system (PC-DOS) is responsible for further processing and storage of the measurement data.
In order to cope with the problem of real-time capability in the data acquisition the Z80 subcomputer includes a ROM-resident FORTH operating system and a measurement program stored in RAM, which can be adapted to the respective experimental conditions.
The two computers are coupled asynchronously via several hardware FIFOs (First-In-First-Out) which allows buffering and time decoupling of the two computers is guaranteed. The connection between the Z80 and the PC is a 16-bit wide and 128-byte deep data path, which is controlled by a “two-wire handshake”. The maximum data rate of the FIFOs is approx. 1 MHz, which ensures a high measurement data transfer rate. The connection from the PC to the Z80 for initialization, parameter and measurement program transfer is designed to be 8 bits wide and 128 bytes deep.
The timing for the experiment is controlled via interrupt-gene Z80-CTCs (Counter-Timer-Circuit), which allows a fast processing of fast occurring measurement signals is made possible. If necessary, the measurement data can be stored temporarily in a RAM buffer, if the PC is busy with “user I/O”.
Interfacesystem
The interface bus system represents the actual interface to the physical experiment. Due to its universal bus structure and the modularity of the measurement plug-in units, one is not specific “measurement problem”. By specific use of the modules and the appropriate choice of measurement programs, the setup can be quickly changed, for example, from an optical (LASER) to an radio-frequency (RF) experiment.
A later expandability of the measuring system was taken into account by making the interface bus as universal as possible:
- 16 data-OUT lines: DAS => Experiment
- 16 data-IN lines: Experiment => DAS
- 8 address lines: selection of 256 different measuring modules
- 8 Control lines: control of the different measuring modules
The individual modules consist of counters (TTL or ECL technology, 32 bit, max. 150 MHz), VFC card (Voltage-to-Frequency Converter), high-frequency decade driver (BCD, 10 bits in parallel), 8 single-bit IN (Instrumentation Amplifier), 8 single-bit OUT cards. An extension e.g. by A/D– or D/A-converter boards is possible at any time.
Measured spectrum
References
- International Business Machines Corp.
- Texas Instruments, SN72172, SN72173, Data Sheet
- Hewlett Packard General Purpose Interface Bus (GPIB)
- TEKTRONIX, Model 2230, 100 MHz storage oscilloscope
- Hewlett Packard, Model HP 3561 A, dynamic signal analyzer
- Burr Brown, Voltage-to-frequency converter, VG 62 Data Sheet
- SCHOMANDL rf decade, type MG 520M (1 520 MHz)
- LMI FORTH, Version 3.0 Reference Manual, Laboratory Microsystems, Inc., P.O. Box 10430 Marina del Rey, CA 90295, USA
- Turbo Pascal, Version 3.0 Reference Manual, Borland International, 4585 Scotts Valley Drive, Scotts Valley, CA 95066, USA
Retrospective
GitHub repositories
- github.com/ThomasFabula/Diploma_Physics
- github.com/ThomasFabula/Forth_Z80
- github.com/ThomasFabula/ZIRKON
- github.com/ThomasFabula/Diploma_DWG
- github.com/ThomasFabula/Atomic-Physics
Further information