Editing Data General Nova (section)

====Special instructions====
These instructions performed various CPU control and status functions. All of them were actually shorthand mnemonics for I/O instructions on channel 63, the CPU's self-referential I/O channel.
* {{code|INTA}} — interrupt acknowledge. Transferred the channel number of the interrupting device to the specified accumulator.
* {{code|INTDS}} — disabled all interrupts
* {{code|INTEN}} — enabled all interrupts
* {{code|IORST}} — I/O reset. Sent a reset signal on the I/O bus, which stopped all I/O, disabled interrupts and cleared all pending interrupts.
* {{code|MSKO}} — mask out. Used the contents of the specified accumulator to set up the interrupt mask. How the mask was interpreted was up to the implementation of each I/O device. Some devices could not be masked.
* {{code|READS}} — transferred the contents of the 16 front panel data switches to the specified accumulator.
* {{code|HALT}} — stopped the CPU. Once halted, the CPU could be made to start again only by manual intervention at the front panel.