Student Projects
Contact Information
University: Università degli Studi di Salerno
Team Member(s): Cappetta Carmine, Iannuzzi Luca, Peluso Roberto Maurizio
Faculty Advisors: dr. Paolillo Alfredo, dr. Pietrosanto Antonio
Email Address: cappetta.carmine@gmail.com
Country: Italy
Project Information
Title:
Handshake's Protocol Analysis on a 488.2 Bus, Italy
Description:
The project’s aims are to design an automatic measurement system that measures peculiar time intervals in a handshake protocol between a Controller in Charge and a device, connected to an IEEE 488.2 bus, also known as GPIB bus, using a digital oscilloscope.
Products:
Labview
The Challenge:
It was decided to monitor in particular three lines of the total twenty-four of the 488.2 interface:
1. the Data Valid line (DAV) which indicates the presence of new data available for acquisition on the line;
2. the Not Ready For Data line (NRFD) which indicates the readiness of the device to accept a new data;
3. the Not Data Accepted (NDAC) which indicates the correct reception of the data by the device.
Monitoring these three signals it is possible to derive several information about the transmission of the data through the bus and the of the signals too.
Brief Description of the 488.2 Bus Handshake Protocol
The communication protocol on a IEEE 488.2 bus is started by a System Controller (SC) that gives control to a Controller in Charge (CiC) or retains it (taking the CiC role itself); then the CiC send on the bus the data needed for a correct communication, in fact it first provides the addressing for talker and listeners, controlling the talker’s uniqueness, then yields to the talker the role of source handshake and allows the communication between the talker and the addressed listeners.
The communication then proceeds with an exchange of data from the talker to the addressed listeners at the end of which the CiC could start a new operation addressing new listeners and a new talker. In any moment the SC can interrupt the communication, if it is necessary, and perform different operations (i.e. it could start a poll if it has received a service request from a device).
Using the DAV, NRFD and NDAC signals it is possible to know how long it takes to transfer one byte from the talker to all the listeners and other information useful to characterize the transmission of the information, such as the data rate, that is the time between one bit transfer and the following. In fact the DAV is initially false (remember that the IEEE 488 operates in negative logic) and becomes true only when NRFD switches high, which means that all the devices are ready to accept the current data on the bus; then the DAV remains true as long as all the devices accept the data, in other words, as long as the NDAC become false (which means that all the devices have accepted the data); at this point a new data transmission could start and the process repeats until the talker hasn’t finished the entire transmission or the SC takes the control of the bus.
Figure 1
This time is influenced by the number of devices connected and, of course, their features, as will be evident afterwards.
The Solution:
Design of the Measurement System
The measurement system is composed of three instruments connected by an IEEE 488.2 bus:
- 1. a Personal Computer (PC);
- 2. a digital oscilloscope (TDS540D);
- 3. a digital multimeter (Fluke 45).
The PC is the SC and CiC of the measurement system, it is connected to the oscilloscope and the multimeter, while a third IEEE 488 cable, also connected to the PC, is used to gather the three signals (DAV, NRFD, NDAC) and lead them to the oscilloscope’s channels to collect the waveforms and determine the times of interest.
Figure 2 Figure 3
Flow Chart
Software Definition and Results
The software is structured on the basis of an event architecture; the user can execute the different measurements by clicking the different buttons in the front panel and then the software returns not only the values of the measures and their uncertainty, but also the waveforms acquired by the oscilloscope. There are two kind of measures that the user can execute: one on the transmission of a single byte, showing all three signals and their characteristic times and the other on several data transmission to evaluate the data rate of the system; for each of these measurements the user could also choose the method for the uncertainty evaluation (A Class / B Class).
The user could also decide to evaluate the performances of the only oscilloscope or of the entire system (oscilloscope and multimeter). In the latter case it is possible to see, as expected, that the system is slower than in the former case, due to introduction of a slower device (the multimeter) in the measurement system (remember that in the IEEE 488 protocol the data transmission is influenced by the slower device connected to the bus).
A modular structure of the software is also provided to ensure easiness in reading, debugging and modifying the software itself, in case it is needed.
Figure 4 – Software’s Front Panel
Figure 5 – Measurements’ Results
References
[1] Evaluation of measurement data – Guide to the expression of uncertainty in measurement – JCGM 100:2008
[2] Sistemi automatici di misura e acquisizione dati – Pirani S., 1990
Nominate Your Professor: (optional)
Dr. Alfredo Paolillo, PhD, Assistant Professor of Electronic Measurements, he helped us in many ways and he teached us how to properly use Labview too. He has been a guide for us, together with Prof. Antonio Pietrosanto, PhD, Full Professor of Electrical and Electronic Measurements, he stimulated us during the entire project's realization.
