High speed analogue-digital conversion and addressable trigger generation on the IEEE 488-1975 interface bus

SINCE specifications were published in 1975, the IEEE 488-1975 interface bus (also called the g.p.i.b, or h.p.i.b.) has become available in an increasing number of small digital computers. These computers are attractive for use in biological and medical laboratories owing to their flexibility and relatively low cost. Of these devices, those that allow easy manipulation of 2and 3-dimensional graphs are especially useful owing to their Iapid visual presentation of data. However, it has been difficult to use these computers for the direct control and analysis of experiments. The ~readily available methods of analogue-digital conversion tend to be slow and no commercial method exists for the control of peripheral devices that do not support the g.p.i.b. We have developed and tested two devices that solve these problems and have applied them to the analysis of electrophysiologic data. The first circuit is an analoguedigital convertor that transmits over the g.p.i.b, the arithmetic mean of a preset number of samples. This process allows computers with rather slow g.p.i.b, rates to resolve relatively rapid signals, such as the action potentials of neurones, electromyogram recordings, or evoked ventral root potentials. The second device converts g.p.i.b, addresses into t.t.l. (transistor-transistor logic) compatible trigger pulses that can then be used for remote control of peripheral devices that do not utilise the g.p.i.b., such as stimulators or tape recorders.