SPX-MPU is a 6-layer pc board with power/ground layers in the middle. On some pc boards it is easy to see the inner layers clearly. This is how schematics are derived:
- Remove all components.
- Take high resolution photos of the bare board, component side and solder side.
- Overlay the component layer with the solder layer in Photoshop
- Manually trace the signals, switching layer in Photoshop as the trace switches side. Use continuity meter to verify connections where needed.
There are two sheets of C size schematics and one size B schematic. Please note these are schematics of the original pc board. They do not reflect subsequent engineering changes.
CPU/memory schematic (updated 11/25/17),
I/O schematic (updated 11/25/17).
Reset logic schematic (updated 11/25/17).