Control of peripheral devices with a general-purpose processor and universal adaptors

Abstract

Large-scale integration is difficult to apply in the area of peripheral-device control units. This is because frequent design changes result in long design times and limited production runs. The paper presents a solution to this problem, in which the control of a group of peripheral devices is shared between one general purpose microprocessor and a number of `universal adaptors' (u.a.s) all made to the same design. The u.a.s contain certain mandatory features, such as output registers and circuits for recognising addressing information and simple instructions sent from the processor. They also contain two special-purpose stored-program structures aimed at relieving the load on the processor and its input-output interface. One, called the sense unit, detects specified external conditions and interrupts the processor when they occur. The second, called the sequence unit, carries out simple input-output routines that involve the detection of external events and timing or counting. The paper gives details of the facilities these units provide and discusses the reasons for them. Their programs total 9 bytes and are loaded by the processor as needed. A system suitable for low-and medium-speed devices has been built and successfully demonstrated. In this, all the logic and storage functions of the u.a. are provided on a single m.o.s.t. chip containing about 6000 transistors. The u.a. logic circuits and the interface between u.a.s and the processor operate in the serial mode.