NuXT1-MultiIO

a WIP Multi-I/O card for the NuXT 1.2 XT clone from Monotech.

The hardware for this is licenced under the CERN Open Hardware Licence Version 2 – Strongly Reciprocal in line with the original licences from open hardware projects from which this project is derived.

Features

• a TimeKeeper - a battery-backed Real Time Clock and nonvolatile storage, cribbed from Aitor Gómez García's RTC8088 project.
• a Printer Interface, or Parallel Port - probably based off the original Printer Interface Card at this point, or possibly the IBM Serial/Parallel Card
• two Serial ports, corresponding to COM2 and COM3 - using the 16550 UART for higher-speed links, but based either on application notes or the IBM Serial/Parallel Card.
• one of the above Serial ports may connect directly to a RasPi Zero, either to provide a slightly more modern machine to minicom to, or to serve a ppp link for internet access.

Purpose

The v1.2 NuXT is an excellent computer with just a few missing features for convenience. The NuXT v2 has improved on this, but there is still an installed base of NuXT v1 devices that can benefit from a semi-modern multi-I/O solution; existing multi-I/O cards may also have features that are superfluous or conflict with onboard peripherals.

I (Horst Burkhardt) determined that what I primarily needed from an expansion card was a method of network connectivity, (best served by a serial link), a parallel port, and that I would like a Real Time Clock. If I can find documentation on the original IBM XMA (Expanded Memory Adaptor) or a similar card, I would also be willing to add RAM on this card, in order to provide enough space for a RAMdisk.

Questions

Why not Ethernet?

An 8088 or an NEC V20 with half a megabyte of memory just doesn't need ethernet. Quite frankly, a 10Mbps link will often work poorly on a modern Gigabit-capable switch. And I don't really relish making CAT5 cross-over cables. A serial link at 115200 baud, which is roughly where a 16550 tops out, is more than fast enough to transfer files to an 8088. It's also a lot computationally simpler than managing an ethernet link, so despite the potential for higher transfer speeds from an ethernet NIC, the real-world gains are dubious.

Why aren't you taking advantage of $(the hot new thing)?

Because I don't care. It's not important. This device must be reliable, simple to troubleshoot, and most importantly, I have to understand it. If a new device is compelling enough, I'm happy to try and work with it, but I'm not putting my name on something untested and unproven.

Why are you like this?

Some very clever people have tried to work that one out, and failed. For now, you're stuck with me.