Since the mid-1980s and the announcement of the Sinclair QL, which 'never happened', I have always been interested in the Motorola 68000. My means did not allow me to buy a Mac, but I could have buy a QL. In short...
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And then the time passed and I got down to the PC. So I never owned, either, atari of the ST range :
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Then the years passed again and in the early 2000s, I decided to develop my own 68000 board. Nothing very complicated. A 68000, RAM, ROM, real time clock, LCD display and serial port plus a small extension connector. Which gives this schematic:
This schematic has some small errors, especially on the side of the MC68B50 serial converter. However, nothing serious since once corrected on the board, the system worked fairly quickly.
The PCB :
Originally, this board was designed to operate at 10MHz. Once the operation was validated, I have not touched this system since 2004. It has now been over 15 years.
Since a few months, I decided to take up the subject of processor boards. This is the reason of this blog dedicated to retro-computing, with current technology.
Fortunately, I kept all of the project files. In addition, all the logic of the board is contained in a PLD so that it is possible to modify the behavior of the system.
Wen I wanted to put this board back into service, I noticed that it no longer included the 10MHz oscillator.
Impossible to find him. On the other hand I had a version of 16MHz. So I looked to see if it was possible to adapt the board to this new frequency.
As I am using EPROM emulators with very short access time, I have not changed the DTACK delay. I only modified the generation of the Baud Rate and took the opportunity to go from 9600 baud to 19200 baud.
At 16MHz, the clock speed is a little too fast for the 68B50 which is given for 1.5MHZ. Well, 1.6MHz should pass.
And here we are!
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This emulator can emulate up to 27C040 type EPROMs. Originally this board was intended to work with AT29C040A type Flashes. I had to accommodate the differences between these two types of circuits.
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