Data transfers between the 502 and its peripheral equipment are carried out with the aid of a partially automatic facility which is referred to as Autonomous Data Transfer. Once this facility has been initiated by a programmed instruction, it operates completely independently of whichever programme is currently being obeyed. Several peripheral devices may operate independently, each making use of the Autonomous Data Transfer facility, and a built-in fixed priority arrangement prevents confusion in the case of simultaneous demands by two or more external units.
An interruption for the transfer of data casues only a short delay in the execution of the current programme. This delay is simply the time needed to interrogate a fixed location in the store, in order to ascertain the required transfer location, and to transfer one or two words. The current programme is not otherwise affected.
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