[comp.sys.ibm.pc] AT Interrupt Controller Programming Question

hennesse@dtrc.dt.navy.mil (Hennessey) (12/27/89)

I have a interrupt-driven serial port driver that works fine on the PC, but
does not work on an AT. It seems that some interrupt occurs, and the controller
is not reset, causing a lack of interrupts.

If I remember correctly, the AT computer uses 2 8259A interrupt controllers.,
instead of one like the PC.

I need programming details: 

  Where is the second chip (I/O addresses A0 and A1???)

  What does the second chip service?

  How do you set the interrupt mask register (I/O port 21 on the PC)

  How do you reset after servicing the interrupt?

Thanks...

Dave (301) 227-1400