The μPAC-5xx7(D) series is a palm-size programmable automation controller. It has a 80186 CPU, SRAM, Flash, Ethernet port, RS-232 and RS-485 port. With a DOS-like OS (MiniOS7) and a developed firmware running inside, it can act like a small PC. 

For hardware expansion, it also supports an I/O expansion bus. The I/O expansion bus can be used to implement various I/O functions such as DI, DO,A/D, D/A, Timer/Counter, UART, and other I/O functions. Nearly all kinds of I/O functions can be implemented by this bus. But the bus can support only one board. There are more than 10 boards available for 
μPAC-5xx7(D) series, you can choose one of them to expand hardware features.