On 14/06/2018 22:38, Nejat Dilek wrote: > Do CIA chips really keep the NMI low if they don't get an ACK? I don't > think so. Yes, really. The CIA doesn't know that it's interrupt output is connected to the NMI or IRQ line, it just keeps the output low until you acknowledge the condition. In the case of the IRQ the CPU will take an interrupt if the line is low and IRQs haven't been masked, it then automatically masks IRQs so it won't keep triggering in the handler. If you don't acknowledge it then when IRQS are unmasked then you will get another interrupt. As NMIs can't be masked and you don't want it to restart the handler every time it checks the NMI line is low before running an instruction, it only looks for high to low transitions.Received on 2018-06-15 01:01:11
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