The 25¢ Apple II Real Time Clock (1981)

This philosophy of doing things the easy way makes one wonder at the prices that are being charged for some of the peripheral boards for the Apple, particularly real time clocks. When either one of these pins is grounded, the processor finishes the machine language instruction it is currently working on, saves the program counter and processor status register onto the stack, (if you don’t know what that means it isn’t important) and jumps to a program somewhere in memory called an interrupt handling routine or interrupt handler. The second difference is that NMI and IRQ have their interrupt handlers at different places in memory.

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