Bus grant line

Bus grant lines are used in a number of bus architectures (for example, the UNIBUS and QBUS) for the CPU to communicate to devices that their request for interrupts and DMA have been granted (hence the name).

They are wired in series, so that one device's 'grant out' line is connected to the next device's 'grant in' line, starting the the CPU's 'grant out' line. When a device sees a 'granted' pulse on one of its grant in lines, if the device had requested a DMA/interrupt, it 'consumes' the grant pulse, and goes on to do the type of operation it requested; if it was not requesting that type of operation, it 'passes' the grant by generating a 'granted' pulse on its grant out line.