1. An input/output pulse processing apparatus having a plurality of input/output (I/O) pins, coupled to a microcomputer through buses for processing pulses in accordance with a task required by the microcomputer, said apparatus comprising: I/O task register means having a task register group consisting of a plurality of task registers, each of which store a task microinstruction supplied from the microcomputer through said buses, said microinstructions being necessary for executing a task required by the microcomputer, and an address signal generator for counting an internal clock and producing address signals for accessing the task register group on the basis of the counting result, wherein the task microinstructions are read out successively from the task register group to execute the task required by the microcomputer in accordance with said counting result; wherein each of the task microinstructions includes an instruction code specifying one of a plurality of basic I/O processing operations, a code for specifying at least one register necessary for executing a basic I/O processing operation and a code for specifying at least one of the I/O pins, through which an input signal is taken into or an output signal is delivered from said I/O pulse processing apparatus, and wherein the task required by the microcomputer is completed by a combination of task microinstructions selected and supplied by the microcomputer; task decoding means connected to said I/O task register means for receiving the successively read-out task microinstructions and for producing control signals by decoding the read-out task microinstructions; I/O operation means, controllably coupled to said task decoding means, including a register group made up of a plurality of registers, each of which is capable of being specified by control signals produced as the basis of a read-out task microinstruction and performing a register function necessary for the execution of the basic I/O processing operation specified by an instruction code of the read-out task microinstruction, and an arithmetic unit connected to the register group through internal buses for performing an arithmetic operation on the basis of data from the specified registers in accordance with the control signals produced by decoding the read-out task microinstruction in said task decoding means; and I/O pin selector means selecting at least one of the I/O pins and connecting the selected pin with said task decoding means or said I/O operation means, under control of the control signals produced on the basis of a pin specifying code of the read-out task microinstruction.