>Ruud Baltissen wrote: >> The SRC revealed that the unused port A is read to clear the IRQ caused by >> the ATN line. I can disable IRQ with the instruction SEI. If during the time >> IRQ that is disabled an ATN shows up, the IRQ-input of the 6502 is negated. >> Question: if I enable IRQ again with CLI, will this IRQ still be handled? >> >> AFAIK the answer is "Yes", but I want a conformation please. >> >The IRQ is not "cached" in any way, but if the IRQ line is still active >(i.e. negated) when you do the CLI (as it would be unless you explicitly >cleared the ATN condition by reading port A before the CLI), the IRQ >will be taken of course. Also the CPU has to be "awake" to record the fact that an IRQ has occurred. It is not latched in hardware in any way. This is different to an NMI which can occur whilst the CPU is supsended (eg during a DMA) and will be acted upon once it is restarted. PLEASE TAKE NOTE: The contents of this email (including any attachments) may be privileged and confidential. Any unauthorised use of the contents is expressly prohibited. If you have received this email in error, please advise us immediately (you can contact us by telephone on +61 8 9441 2311 by reverse charge) and then permanently delete this email together with any attachments. We appreciate your co-operation. Whilst Orbital endeavours to take reasonable care to ensure that this email and any attachments are free from viruses or other defects, Orbital does not represent or warrant that such is explicitly the case (C) 2000: Orbital Engine Company (Australia) PTY LTD and its affiliates Message was sent through the cbm-hackers mailing list
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