The 16C752 datasheet says - if you read it carefully enough - that the INTA and INTB outputs are "high impedance after reset". That wouldn't have been a problem if they had been wire-ORd with the /IRQ, but in original intel strangeness, they are active high, so I have open collector output inverters on those signals. And they read high impedance as high, thus pulling /IRQ low, resulting in an infinite interrupt loop. Argh.
The 16C752 datasheet says - if you read it carefully enough - that the INTA and INTB outputs are "high impedance after reset". That wouldn't have been a problem if they had been wire-ORd with the /IRQ, but in original intel strangeness, they are active high, so I have open collector output inverters on those signals. And they read high impedance as high, thus pulling /IRQ low, resulting in an infinite interrupt loop. Argh.