All, On 5/27/05, James Fogg <James at jdfogg.com> wrote: Please excuse the errors in this description. I am working from memory and I last read the Q22 bus documentation a couple of years ago. The grant continuity cards pass the interrupt signal through the slots where there are no cards. The Q22 bus is designed to have interrupt priority determined by physical location in the card cage. Cards electrically closer to the CPU have a higher priority than cards that are further away. The interrupt lines pass through each of the cards in the card cage. This means that for the interrupts to work, the card cage has to be fully populated between the last card in the card cage and the CPU. This posed a problem when working with full height and half height Q22 bus boards. A card cage configuration may result in a (or several) half height gap(s) in the card cage. A grant continuity card is used in this case to pass the interrupt signals over the gap while adding no additional logic. To my knowledge, grant continuity cards were also used when a single card was removed. This eliminated the need to move the remainder of the cards in the card cage. Hope this makes things a little bit clearer. Good luck. Simon -- ------------------------------------------------------------------------ "Well, an engineer is not concerned with the truth; that is left to philosophers and theologians: the prime concern of an engineer is the utility of the final product." Lectures on the Electrical Properties of Materials, L.Solymar, D.Walsh