The goal of this project was to replicate much of the functionality of the original, but in much less space, with far fewer components, and with simpler power requirements. This single-board-computer (SBC) has a 10 MHz MC68008 CPU, 512 KB of RAM, 512 KB of in-system-programmable flash ROM, two serial ports with adjustable baud rates up to 115200, a 4-bit input port with DIP switches, and an 8-bit output port with vintage TIL311 hex displays. The source for the original TUTOR monitor is available and will be ported to this platform.
A novel feature of this SBC is that the usual (and somewhat elaborate) 68K reset circuitry has been consolidated into a single 8-pin PIC12 MCU. This includes power-on reset generation, manual pushbutton reset switch debouncing, open-drain drivers and pull-up resistors for the HALT and RESET pins, and buffering for the HALT LED. A GAL22V10 PLD provides 20 MHz clock oscillator division to 10 MHz, reset vector remapping, and address decoding for the rest of the system. The fuse map for this PLD was generated using a home-brew assembler. Two serial ports are provided on FTDI TTL-232R cable-compatible headers for communication with a PC. 5-volt power is provided via either of the serial port headers, or via a barrel jack. A built-in bootloader capable of reading Motorola S-records from either serial port into RAM is provided in flash. With the exception of a handful of surface-mount decoupling capacitors and pull-up resistors, the design is entirely through-hole.
There are two accessories for the system. The first is a PIC18-based flash memory programmer. This is used for initial out-of-circuit programming of the AM29F040B flash memory, until the system firmware is sophisticated enough to be able to provide in-system flash programming on its own. The second is a TTL-to-RS232 converter that plugs into either serial port header to provide an interface for an external DEC VT510 terminal.
A Motorola-compatible cross-platform assembler is also being developed from scratch for use with this project. There are nearly half a million legal 68000 instruction/addressing mode combinations!
The PCB is available here:
The code for the Halt+Reset PIC can be found here:
The JEDEC file for the GAL will be added to GitHub as soon as I can find it!