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RCBUS to USB Adapter

A simple CH375/6 based adapter

etchedpixelsEtchedPixels
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The CH375 and CH376 are USB interfaces with an 8bit CPU interface. They are not particularly fast but are good enough for the kind of USB usages an 8bit machine will have. The devices also have a mode in which they act as a semi-smart USB storage adapter and do much of the protocol work for you.
This board provides an adapter between the off the shelf CH375/6 modules and the RCbus.

The CH375 modules available off ebay generally follow a common pinout and have a jumper to switch between serial and 8bit mode. The 8bit bus interface looks exactly like the 8080/Z80 style bus and the only logic on the adapter itself is the chip select generation.

Note that the port defaults to 0xFF and the jumpers set bits of the address to zero. As most adapters work the other way this makes it easy to slot these into other bits of the I.O map. The Fuzix drivers expect the device on 0xBE/0xBF (bottom but one jumper installed only).

ch375.tar.gz

Kicad files

gzip - 181.77 kB - 08/29/2023 at 16:44

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ch375.pdf

Schematic

Adobe Portable Document Format - 48.46 kB - 08/29/2023 at 16:44

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  • Now available from Z80Kits

    EtchedPixels • 01/03/2024 at 12:30 • 0 comments

    You can now get a kit for a CH375/6 board based on this design from z80kits.com

    Software support is also included in ROMWBW 3.4

  • Initial Working Setup

    EtchedPixels • 08/29/2023 at 17:22 • 0 comments

    Another PCB from PCBway. mostly because the one button make your PCB happen Kicad add on is go good for lazy people. There is not a lot on it as you can see - just address decoders. The adapter goes onto the connector facing back towards the board so the USB is in the PCB sandwich. That as I hoped means it fits a single slot on the more generously spaced backplanes.

    The hardware turns out to be easy, the software not so. The documentation isn't very clear and the chip behaviour also turns out to have a few undocumented "and then wait a bit" cases if you want the right results.


    It is now working with an initial Fuzix driver running on my 8085 system.

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EtchedPixels wrote 10/20/2023 at 13:38 • point

The current driver just uses the block device mode on the CH375/6 so it's actually a tiny tiny piece of code. Some day I might try doing full USB. Someone was doing that for the Tandy COCO3 with NitrOS9 but I've not heard anything recently about how it is going

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Dean Netherton wrote 10/19/2023 at 22:06 • point

Cool stuff.  I have been working on something similar for my series of RC2014/MSX boards.
I had to put everything on hold for most of this year - but I have got back into my project in earnest recently - in the process of documenting all it.

I found the software the hardest part - learning all about USB/UFI/SCSI has been a journey... 

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