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SLSI wanted to add additional functionality to their language lab. The system was hard wired for specific functions. They wanted to add a small control board that would mimic the user listening to a sequence of students. Also, the students are assigned to one of 8 different program sources. These assignments were not saved when the system was shut down so they would have to be reloaded on each use.
The final product is shown below:
The control panel actually watches what the user does and maintains the current state. It then can maintain a list if students and their program assignments. The state of 56 different switches are monitored or controlled by the board. The "Auto" switch will cause the system to monitor students assigned to one of the program sources. The time LED display sets the number of seconds to monitor each student. The "Next" switch allows manual control. The "Save" and "Load" switches allow program assignments to be saved or loaded from a EEPROM.
The board consists of a Motorola 68HC711 microprocessor, a small serial EEPROM and 2-digit multiplexed display. Additional logic allows the board to read or fake key presses of the rest of the system. Software was a mix of 'C' and assembly language. A PC application allows the board to be programmed without the need of a device programmer.
I added a test feature. This was to test the functionality of the Auto monitor board. It steps through all of the possible switch controls of the system. This test can also be used to test the system.
Overall, the board was successful. There was a small problem with the first board. This was mainly due to not having a complete understanding of how the system operates. This is a complex system that is difficult to understand from the documentation at the time (has since been better documented.) The initial problem was fixed by a quick redesign of some of the logic.
The board works well in the system. Originally it was intended as an add-on, but has been made part of the standard system. The success of this project led to several future projects for SLSI. These projects have been additional add-ons and fixes for some minor problems in the rest of the system. The continued successes, have led to a new project to redesign the entire system using a PC to control the system over a network.