A Teaching Gas Chromatograph/Microcomputer Interface Using the General-Purpose Interface Bus Kathy J.
Table 1. Enzyme Kinetics: Appropriate Variables to Plot and Resultant Slope-and lntercept tor Each Linear Form of Eqn. (2). X Method
Axis
Y Axis
Intercept Slop
( Y Axis)
Dien. Ronald S. Bell, and Michael D. Morris University of Michigan Ann Arbor. MI 48109
In this communication we descrihe a simple and inexpensive interface svstem that nuts a teachine eas chromatoeranh on the genera"l purpose interface bus @FIB). GPIB ;oris are available for all the standard laboraton, mini-commters and for many "personal" computers, including the Commodore PET, the Apple 11, the HP-85 and any computer using the S-100 bus. At present, there are commercially available spectrophotometers, chromatographs, pH meters and other chemical instruments that are GPIB-compatible. In addition, a wide variety of electronic test and display equipment, in-
cluding digital voltmeters, counter-timers, function generators and point plotters are available interfaced to this bus. The general purpose interface bus standard, also called IEEE Standard 488-1978 (or just IEEE-4881, specifies data formats and control protocols for interfacing instruments to computers, as well as connector style and pin placement (27-29).Thus, any instrument obeying the standard can he immediately plugged into any computer that obeys it. Moreover, the protocol specifies hoth hardware and software standards for connectina- 15 instruments plus the control instrument together. The interface bus consists of 16 lines, functionally divided into three groups. These are eight data lines, three transfer control lines, and five general interface management lines. Data is transmitted one byte (8 bits) at a time over the bidirectional data bus. If more than 8 bits of data are being transferred. it must he sent over the bus one bvte at a time. ~-- ~ - ~ The data lines are also used as address lines toidentify each device. Whether sienals on these lines are interpreted as data or device addressesdepends on the signals on
