Category Archives: FPGA

Full multiplexed display for RC2017/10

I’ve now got full multiplexed display operating on the breadboard prototype for my RC2017/10 project: I also shot a brief video showing chaning hexadecimal values. There are six 5×7 displays, physically all in one column to fit the breadboard, but … Continue reading

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RC2017/10 finished wiring LED matrix

I finally finished wiring the LED displays on the breadboard prototype. What a mess! The LTP-305HR displays are still being driven basically statically, with only one column of LEDs (on both logical rows) being illuminated at a time, and only … Continue reading

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More LED matrix prototyping

I’ve added a second breadboard to prototype with all six LTP-705HR displays, and the additional sink and source driver needed. The matrix is wired, but not all of the drivers are hooked up.

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FPGA-Elf display drivers and multiplexing

For my previous FPGA-Elf, I used actual hexadecimal displays as per the Popular Electronics construction article. The only hexadecimal LED displays still made are from Broadcom/Avago, don’t have the integral red filter, and cost around $40 each. Used or NOS … Continue reading

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RC2017/10 project: affordable FPGA-Elf

For the RC2017/10 RetroChallenge, I will update my FPGA-Elf to run on a relatively inexpensive FPGA board, and make PCBs to provide the necessary I/O interfaces.  I plan to add the equivalent of the CDP1861 “PIXIE” graphics. At the conclusion … Continue reading

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Fixed a bug in the FPGA-Elf

My friend Ken pointed out that unlike a real Elf, my FPGA-Elf didn’t display the contents of memory if you repeatedly press the input button while in load mode with memory protect enabled.  At first I couldn’t figure out how … Continue reading

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FPGA-Elf is 100 times faster than original COSMAC Elf

The original COSMAC Elf ran at 1 to 2 MHz.  Every machine cycle required eight oscillator cycles, and each instruction required two or three machine cycles, so each instruction took 8 to 12 microseconds at 2 MHz, or 16 to … Continue reading

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Video of demo of FPGA-Elf

Richard Ottosen used my cell phone to shoot a short video of me demonstrating the FPGA-Elf, toggling in and running the dice demo. Thanks to Jim Donnelly, Richard Ottosen, and Jim Phillips for helping me put together the FPGA-Elf front … Continue reading

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New demo for FPGA-Elf: dice

I needed a demo program for the FPGA-Elf that was at least a little more interesting than simply counting, so I wrote a dice program.  When you press the input button, it simulates rolling a pair of six-sided dice.  Perfect … Continue reading

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FPGA-Elf now fully working!

After much gnashing of teeth and pulling of hair, I finally figured out what was causing load mode to fail on the real hardware despite working on the simulator.  My “next state” logic didn’t have a default value, so both … Continue reading

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