IOT Instruction

• Instruction format 6XXY.
• XX is address of device. Peripheral has normal address with jumpers or switches to select alternate address. Some normal addresses conflict.
• Y is operation to perform. Determined by peripheral. Can load or OR data with AC, skip, transfer AC to peripheral register, set control bits.
• Peripherals can run independently performing single or three cycle data breaks (DMA). Three cycle data breaks uses memory for word count and address and processor updates. Saved logic but slower.
• Memory past 4k was an option and used IOT instructions.
• Interrupt control also used IOT instructions. One interrupt and needed to poll devices to determine which generated interrupt.