Concurrent subsystem diagnostics and i/o controller

Claim 1

In interfacing circuits for generating an anomalous indication from a subsystem in response to a requesting signal from a controlling data processing system interconnected with said subsystem via said interfacing circuits, means chaining said subsystem to a CPU, means supplying a flag signal, means selectively setting a diagnostic mode, memory means for maintaining a status indication and a flag signal, means gating said status indication, logic means responsive to said requesting signal and another signal to generate a gating signal, the improvement including in combination: AND circuit means jointly responsive to said requesting signal and a flag signal from said subsystem to supply an enabling signal, said subsystem capable of setting said flag signal only when chained to a CPU and in a diagnostic mode of operation, encoding means responsive to said status indication or to said enabling signal to generate a code permutation representing said status indication, and said gating means being responsive to said enabling signal or to said gating signal to gate said code permutation to said CPU.