The Auction Keyboard Network contains up to 250 dedicated keyboards connected together to a RS485 bus. This bus is arbitrated by a Master module connected to PC by a RS232 serial interface.
The access to bus is arbitrated by a “sliding windows” protocol and the reaction time of the whole system is less than 50ms. Thus can be detected the first keystroke from the whole network during the auction procedure.
This system is already installed to more clients in west Europe like the “Pan European Fish Auction Company” from Zeebrugge, Belgium. The auction Keyboard can be seen in the Figure 5.1.
The keyboard is build around an “AT89C52” processor and has the following resources: one RS485 interface, an electronic access key (Dallas Key), the keys and the display with
large 7 segments LED modules, ISP connector for In-Site-Programming of the microcontroller.