Semi-custom-made integrated circuit device

An integrated circuit device fabricated on a semiconductor substrate, said device comprising a plurality of function blocks each achieving a predetermined function and an internal bus system operative to coupled said function blocks, in which one of said function blocks comprises an input-output circuit which is operative to transfer pieces of data information supplied from outside said integrated circuit device to said internal bus system, and a control signal generating circuit responsive to external control signals fed from outside said integrated circuit device and operative to produce a plurality of internal control signals representing respective commands used for a diagnostic operation for another function block, said diagnostic operation being carried out on the basis of said pieces of said data information supplied from outside said integrated circuit device, said external control signal having a test signal for activation of said control signal generating circuit and enabling said input-output circuit to transfer said pieces of said data information to said internal bus system for said diagnostic operation, a write-in command signal and a read-out command signal, said internal control signals having an activation signal which is used for activating at least two circuits forming part of said another function block each specified by one of said pieces of said data information, a write-in enable signal used for causing one of said circuits of said another function block to store another piece of said data information appearing on said internal bus system and a read-out enable signal used for enabling the other of said circuits to deliver a piece of data information to said internal bus system, wherein said at least two circuits of said another function block serve as a transmitting buffer circuit and a receiving buffer circuit, respectively.