• Just a small update on the status of the DIY CPU:

    The circuit design of the main CPU components is completed. The layout was split up in six parts :

    • ALU and Shifter
    • Index Registers
    • General Purpose Registers and Program Counter
    • Flags
    • Clock and External Bus I/O
    • Microcode Sequencer

    Each part occupies an 160x100mm circuit board. The boards are interconnected with pin headers to provide access to the internal data and address bus and to distribute the clock signal.

    DIY CPU PCB Layout

    DIY CPU PCB Layout

    Parallel to the layout the circuit was constructed in a simulation tool to test correct function. To fill the microcode storage with meaningful code, a Delphi program was written to generate the microcode sequences for the opcodes.

    DIY CPU Microcode Generator

    DIY CPU Microcode Generator

    This program was used to implement the microcode for a few basic opcodes which were then used to write a small assembler program that calculates the fifth fibonacci number (see screenshot).

    I’m currently working on some other projects to get some distance from the CPU. This helps to spot errors when looking over it a few weeks later. Then a few additional circuit boards for data I/O and storage/RAM will have to be designed.

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  • (FYI : I am currently not posting the projects in chronological order, because I have so much stuff lying around that I did before I had the blog. So those things will show up from time to time.)

    The 4×4 LED Display was my first project with a two-layer circuitboard layout. The alignment was not 100% optimal, but sufficent. I wanted to make the board as small as possible, so the parts had to be stacked at some places. The square LED’s were painted black on the sides to keep the pixels sharp.

    4x4 LED Matrix Circuit Board (Top)

    4x4 LED Matrix Circuit Board (Top)

    The rows and columns are both controlled by a 4094 Shift&Store-register. The upper four bits control the coloumns and the lower four the rows. So for each frame 4 bytes have to be shifted in. That is done via a QBasic programm that toggles pins on the serialport. Instead it would also be possible to just send the bytes over a serialconnection, but I was to lazy to write code for that.
    To generate the patterns, one can put them together binary by hand. But I choose the easy way again and wrote a Delphi-Program to generate patternfiles, which then would be send to the display by a QBasic programm. (I test all my circuits on old DOS-PCs).

    Here is a video of the display in action. The sequence is preprogrammed…so no actual tetris yet..

    Layout and circuit are here. QBasic sourcecode is too ugly to show. How to shift data into a shiftregister should be easy for everyone who can read the datasheet.

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  • Parallel-to-I²C-Adapter

    Parallel-to-I²C-Adapter

    Just a little circuitboard to interface I²C-chips to the parallel-port.

    I designed the layout so it can fit inside the case of the connector.

    An additional diode to protect LS05 from reverse polarity might be good. (I already ‘converted’ one to smoke 🙁 )

    Eagle5 layout and some simple TurboC++-Code for the adapter can be downloaded here.

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