Added the Pixie chip CDP1861

A project log for FPGA Cosmac ELF

A re-creation of a Cosmic ELF computer, Coded in SpinalHDL

Winston LoweWinston Lowe 01/22/2020 at 09:273 Comments

Today I finished writing and testing the CDP1861 Video Display Controller.  It was a addon for the Cosmac ELF, and was also used in the Cosmac VIP, and the RCA Studio II game console. It has a resolution of 64x128, with software you can change it by redrawing lines which can give you 64x64, and 64x32.

I was able to simulate both the 1802 CPU and 1861 VDC.  and also have the CPU running the driver software for the VDC that help a lot with finale testing.

But most of the testing was done while feeding in simulated signals.

The chip are pretty simple, It uses two counters, one for counting lines(Line Counter) and the other for counting machine cycles (MC Counter).

This is a picture of the video output from the 1861 VDC running on my FPGA, using the classic test program that was apart of the article on adding it to the Cosmac Elf in the Popular Electronics magazine. You can also see a video of the output on my instagram


zpekic wrote 01/24/2020 at 07:30 point

Congrats for conquering another one from this list: - which one is next? That MUL/DIV unit CDP1855 looks very interesting :-)

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Winston Lowe wrote 01/26/2020 at 00:06 point

I think at some point i'll work on making the COMX computer, since there are some games for that system so that means I will need to make the CDP1869 and  CDP1870. The CDP1855 cool but is not used in any of the hobbyist systems.

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zpekic wrote 01/26/2020 at 19:24 point

Very true, I have never seen it used on any board, even the much more popular and capable Am9511 (with which I played a bit) only appeared sporadically in few home computers. 1869/1870 seem like very complex devices, can't wait to see your approach and progress - good luck!

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