The current approach is to use the PC as the host machine. This machine will provide a graphical user interface and control the layout at a higher level. The task of controlling the various bits of layout equipment will be delegated to one or more microcontrollers. These controllers will receive commands from the host and will take on the job of interpreting these commands and driving the layout equipment accordingly. The controllers will also return status information to the host. To keep the interface flexible, the serial port of the PC would be used. The two microcontrollers considered were the 68HC11 and the PIC. Eventually, the PIC 16C84 was chosen.
It is evident that more than one PIC based controller will be involved. These controllers can be daisy chained together or put on a bus. The bus configuration was chosen. The serial port of the PC will be used. A communication protocol between the host PC and the controllers will be used.
Each controller will interface to one kind of equipment. So far, the following types of controllers have been identified.
The PIC 16C84 has 13 pins that can be configured as inputs or outputs. Of the 13 inputs/outputs on the PIC, 2 will be used for the communication bus. Of the remaining, 8 will be used to drive the layout equipment. The rest will be used for debugging or auxiliary control lines. Each controller card will have a standard configuration. The construction of cards is described elsewhere.