The IO Window can be used to simulate the PIO CDP1851 or the CDP1852 I/O chips. This is depending on the chosen main CPU board and / or additional selection of the CDP18S660 Memory & I/O board. The window can be activate or deactivated via the 'IO Window' checkbox either in the main Emma 02 window or CDP18S660 Setup window.
The initial window will show both A and B ports as input but when either port is set to output, bit programmable or bi-directional (via the PIO control register, OUT 6) the window will switch to show input (switches active) or output (LEDs active) depending on the mode selected. The same is valid for the STB and RDY input switches and output LEDs which will become active in bit programmable mode.
The interrupt buttons INT 'A' and 'B' will become active when the PIO interrupt is enabled. A press on either button will send an interrupt signal to the emulated CPU and also activate EF1 or EF2.
The PIO is defined on I/O group 8 for the CPU boards and selectable on the CDP18S660.