Digital Input/Output is provided by a 6522 Versatile Interface Adapter (VIA).

The VIA offers two 8 bit ports, of which every line can be individually configured to be an input or an output. Four additional control lines are provided, and these may be set to generate an interrupt if triggered.

Within Amélie, it is expected that port A is used as inputs (for sensing) while port B is used as outputs (for driving motors, relays, etc). The reason for this is that the values present on port A, when read, will be the true values of each pin (regardless of its status as an input or an output), while the values read back from port B are the latched values.

Also contained within the VIA are two 16 bit timers. The first of these is configured to cause an interrupt at 50Hz (or every two centiseconds). This is used to maintain a system 'clock' and control various time-dependant things. Once set up by the BIOS, it should be left to run and not be touched for any reason. If the main crystal ticks at 2MHz then value to be latched into Timer1 is 40,000. If the main crystal ticks at 1.8432MHz (i.e. the ACIA crystal as the master source), then the value to latch into Timer1 is 36,864. In both these cases, the VIA will provide an interrupt exactly 50 times per second; and as the VIA is independently free-running, drift should be minimal (no values are available at present).
The second timer (only loosely implemented in the emulator) is unclaimed by the BIOS and may be used by the application code.

It should be noted that port A bits six and seven are reserved for the implementation of a basic I²C (or IIC) bus. This is provided to talk to an RTC/NVRAM part, as you can see in the picture (this is not currently supported by the emulator). Port A was chosen for this as reading the port will return the actual values of the pins even when the pins are configured as outputs.

The little circuit shown is a Philips PCF8583P. This can act as a real-time clock with 240 bytes of NVRAM, or as 256 bytes of NVRAM. Salvaged from an old VCR, this part happens to be the same as is used in the 'Archimedes' range of computers.
All that is missing from this circuit, and the big space on the board, is the battery - though there is no reason why two AA cells cannot be wired in (in a holder) with a diode to prevent accidental charging.
 
It is possible, however, that the provision of the provision of the Options selector device (at &A200) will mean that an I²C implementation, while providing more flexibility, is not required - at least within the first version of Amélie .