Chip2d ago

Poking around on my RO352, trying to understand the MFM electrical interface. This is the data connector. It’s using a whole uA9638C dual differential line driver for the read side, and a whole 26LS32 quad differential line receiver for the write side (same as a ST-506, actually). I guess there weren’t any more compact options at the time.

#Aprilcot

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I'm poking around because I'm pondering if you could use one of these very common 8-pin RS-485/RS-422 transceivers for this. I'm guessing the answer is no, as it would mean the read and write lines are connected together.
Apr 4 at 12:58amWeb
Show threadChip2d ago
Ah, nevermind. There are full duplex versions. That'll work great.
Show threadChip2d ago

I'm looking at the schematic for David Gesswein's MFM emulator (it's a lot!). https://archive.decromancer.ca/mfm/oshw/RevD_SMT_Edition/MFME-RevD-SMD.pdf. They are in fact using full-duplex RS-485 transceivers for the data.

I'm pondering the control inputs. That emulator and the pico506 use chips to do level shifting on the input, but to my understanding, that should be unnecessary. All of the control signals are open drain, and the RP2040 has selectable schmitt trigger inputs. If you have a 3.3V pull-up, that should work just just as well as 5V as far as the controller's concerned, yeah?