…plus ça ne change pas. Or so they say, anyway — but the design of this computer has certainly changed. The changes are for the better, though: the core (which will be constructed by the students) has been greatly simplified, with as much functionality as possible having been collected into a control panel unit.
Here is the schematic for the “core.” Some more minor changes may yet happen (perhaps another 74LS245 for the control lines etc), but the core design is essentially finalized. The idea is that the core system can run as a “headless” unit, without a control panel: with the addition of 24 LEDs to show the status of the address and data lines, it should look like a real “Hollywood” computer, complete with blinking lights! I’m still skeptical about putting LEDs directly onto the busses, but we’ll see how that works out. If nothing else, they can be driven by three more ’245s.
The control panel (still under construction) will include:
- Rotary hex switches to enter addresses and data;
- An LCD panel to read addresses and data (and perhaps other information);
- Run/Stop, Single-Step, Manual/Auto, Reset, and Write switches;
- An SD card slot and Load/Save switches to back up programs to an SD card; and
- Three PIC microcontrollers to run all of this.
Right now, I’m creating a set of inter-MPU commands, to keep everything in sync. Complete details will be available here once it’s all finished.