Acorn "POST box" display adaptor (0086,804)

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sirbod
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Re: Acorn "POST box" display adaptor (0086,804)

Post by sirbod » Sun Jun 07, 2020 7:46 am

Nice, looks really professional.

As I said back in May, I could make use of one of these to help diagnose my A5000. I've managed to fix all my Acorn machines except that one, which stubbornly refuses to POST.

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myelin
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Re: Acorn "POST box" display adaptor (0086,804)

Post by myelin » Tue Jun 09, 2020 6:16 am

First board soldered... the fine pitch QFP had solder bridges everywhere after reflowing, but thankfully one pass with flux and solder wick picked them all up, so the assembly experience wasn't quite as bad as I thought it might be; still more work than BGA, but not as bad as doing it by hand :)

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The FPGA showed up straight away when I probed the board with Lattice Diamond (+ clone HW-USBN-2A cable), and programmed successfully. I'm lacking one buffer and the micro USB connector, so I can't actually do an end to end test yet, but I got the FPGA to output its internal oscillator on one of the GPIO pins, and it looked all right.

F643539F-AEB0-47B6-9E23-98FD8DFEEEFE.jpeg

Got to play with my new scope while trying out the different drive strength and slew rate settings -- the pic above shows it with the defaults (8mA drive, fast slew). Reducing it to 4mA drive and slow slew made the waveform quite a lot nicer, and the rise time was still < 10ns -- looks more like this:

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Update: The last few bits arrived, and I've got it programmed and pushing the 48MHz clock from the MCU out through an FPGA IO, and it looks good. Pretty much ready to test now, I think!
SW/EE from New Zealand, now in Mountain View, CA, making BBC/Electron hardware projects for fun.
Most interesting: Arcflash, FX2+PiTubeDirect Tube/Cartridge adapter, USB cart interface.

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myelin
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Re: Acorn "POST box" display adaptor (0086,804)

Post by myelin » Thu Jun 11, 2020 7:55 am

This evening I managed to dump out a RISC OS 3.10 ROM image from an A3000, and connect to a Bush IBX250 and almost dump out the ROM image, although with some spurious FFFFFFFF words inserted. Progress!

I’ve found and fixed a bunch of bugs in the C and Verilog, and its already much more reliable than the previous hardware (MCU + xc9536xl). So very nice to have the hot plug output via the 74LCX125 too — not having to worry about power leaking in or out has made this much easier to work with.
SW/EE from New Zealand, now in Mountain View, CA, making BBC/Electron hardware projects for fun.
Most interesting: Arcflash, FX2+PiTubeDirect Tube/Cartridge adapter, USB cart interface.

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myelin
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Re: Acorn "POST box" display adaptor (0086,804)

Post by myelin » Fri Jun 12, 2020 10:20 pm

Here it is running back to back reads of the rom in my IBX250, as a soak test. I’ve seen the occasional failure, but today it’s been happily reading without errors for hours.

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I’m going to try to build up a few more tonight so I can get them sent off. Who wants one?
SW/EE from New Zealand, now in Mountain View, CA, making BBC/Electron hardware projects for fun.
Most interesting: Arcflash, FX2+PiTubeDirect Tube/Cartridge adapter, USB cart interface.

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myelin
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Re: Acorn "POST box" display adaptor (0086,804)

Post by myelin » Sat Jun 13, 2020 6:16 am

That was a pretty successful assembly session... made three more — cleaned out my MCU supply, so I’ll need more before I can build more of these!

16BFBC04-E1A5-4F6D-84EC-7732971F3528.jpeg
SW/EE from New Zealand, now in Mountain View, CA, making BBC/Electron hardware projects for fun.
Most interesting: Arcflash, FX2+PiTubeDirect Tube/Cartridge adapter, USB cart interface.

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myelin
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Re: Acorn "POST box" display adaptor (0086,804)

Post by myelin » Tue Jun 30, 2020 5:50 pm

I've been using this quite a bit on several different machines, and it seems pretty solid. philpem has the first one and will undoubtably have more to say soon, but I think it's safe to start making more of them for others. I've thrown up a post on the "for sale" board; and will assemble these a few at a time whenever there's any demand :)
SW/EE from New Zealand, now in Mountain View, CA, making BBC/Electron hardware projects for fun.
Most interesting: Arcflash, FX2+PiTubeDirect Tube/Cartridge adapter, USB cart interface.

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