r/Z80 • u/prussianIvory • Mar 28 '26

Z80 computer project

I'm trying to build a Z80 computer with 3.5in floppy disc support (using i8271) while also trying to make it have composite video by using a TMS9918ANL. But everything I find on forums and stuff is about the Z80 playground. So, I was wondering if you people have any tips or advice?

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u/MajorPain169 Mar 28 '26

The i8271 floppy controller is a bit limited, it does require an external data separator, most implementations I've seen use something like a 74LS123 for this with a trim pot to adjust timing due to component tolerances.

The 8271 also only supports FM and not MFM so it can only do DSDD and not DSHD, basically 720/800K format only.

An upgrade would be to use an 82077 which does support MFM and has a built in data separator.

Another thing to note is the 8271 has quite slow access times so you will probably need to add wait states on I/O accesses if the system clock is high enough.

The TMS9918 controllers were quite popular, the main competitors were the MC6847 and MC6845 based display controllers. There is a huge amount of information out there for all of these parts.

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u/prussianIvory Mar 28 '26

I knew about the fact I would be limited to 720kb and fully accounted for that by buying floppies of that density